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Hardware support => General topics => Topic started by: LazyGlen on December 19, 2013, 09:45:44 AM

Title: Weatherproofing Moteino's
Post by: LazyGlen on December 19, 2013, 09:45:44 AM
A couple of my pending projects may require sealing up the Moteino. I've seen some suggestions for small enclosures including Felix using hardware store screw boxes and packing tape.

I have recently discovered Polycaprolactone, which is a "low" melting point, bio-degradable and re-useable plastic which is great fun to play with. Available on your neighborhood intertubes under a variety of names (Instamorph, Shapelock, Polymorph...). I think this would be perfect to 'pot' a Moteino with, for electrical insulation purposes, securing wires or weatherproofing. It becomes putty-like at around 60oC and can be formed by hand until it cools and hardens. It does sometimes stick to other surfaces (like a rolling pin if you are making a sheet), I have not tried it against IC's or PCB material yet to see if it sticks to that. I'm thinking that it might even be removable once you decide that you want your Moteino back. Drop the whole thing into a pan of hot water, wait a bit, and peel off the Polycaprolactone to access the Mote'. Perhaps putting a layer of plastic wrap (or a condom) on the Moteino first would make removal easier.

It may also be useful for making programming jigs a little less fragile.

I'm not yet ready to seal up any projects, but thought I would put this out there for anyone who is.

I will update when I get to this point in my project(s).
Title: Re: Weatherproofing Moteino's
Post by: Felix on December 19, 2013, 02:22:25 PM
Thanks!
Is it somewhat like sugru?

FWIW you can make something similar to sugru using silicone and starch: http://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute/
Title: Re: Weatherproofing Moteino's
Post by: kolumkilli on December 19, 2013, 06:30:22 PM
I have been using the Shapelock branded version for years, and I agree, it is pretty great.
It's not like a silicone-based product, when it hardens up it feels more like HDPE or Nylon 6,6.

I've even used it for Moteino enclosures as well!  But I've had limited success with certain applications, mostly for the following reasons:

1) when warm, it flows, so while you can shape it, unless you are using a mold, it continues to deform and you cannot get repeatable dimensions.

2) its flexibility changes with thickness as you are molding it, so you really have to adjust for thin parts cooling off faster than thicker parts.

3) it traps air in bubbles if you knead it and capture some air.  That in itself is not so bad, but if you heat it in water, it will also trap a lot of moisture in similar bubbles.  I would not want to put that next to electronic components (or not directly - if you seal things in plastic first, that may work just fine).

4) because of the above, I do not use water to heat the substance.  It goes from a white color to a near-clear color when it crosses its glass transition temperature, but you do not get any further visual clue about the temperature until it begins to boil, and that occurs at a much much higher temperature.  Heating it in water creates a maximum temperature at 100C so at worst you get scalded, but not using water so as not to trap water is very dangerous.  It can get above 200C very easily, with no visual cue.  And when you grab it, it instantly adheres to your skin, and has a very high heat capacity as well, so burns you and continues to burn you and you cannot remove it except by sacrificing some other fingers.   Even if you have a handy source of cold water, all this will do is harden the outer shell, while the inner part that is adhered to you continues to burn you.

The "stickiness" of the substance seems to be parametric to temperature.  I mean that against ICs and PCBs, but also against glass, and stainless steel, and of course, human skin. 

As you might be able to surmise, #4 above happened to me.  It was because I lost track of the time elapsed while heating.   Stupid of me, I know.  It just got hotter and hotter, with no visual cue.  It was supposed to be just a bit warm... The result was not pretty.  I still don't use water to heat the substance, but now I always check it with a non-contact infrared thermometer, you can get for $10 or $15.  Even if you do use hot or boiling water, you will find that when it is uncomfortably hot but able to be handled, it will be much stickier than when closer to its transition temperature.  I recommend checking the temperature no matter what you are doing.

The stickiness does change after adhesion as well - so while it will stick to glass strongly when really hot, as soon as it cools it can be peeled right off.  That makes it less useful for things where you want to partially embed something in it, that doesn't have a mechanical shape that prevents slippage, especially if under load.

I'd be concerned about the polymer flowing around and under the components if applied directly, and then when/if you remove, it might cause sideways forces that exceed the trace to fiberglass adhesion force, tearing off the components.

Don't get me wrong, the stuff is great, and I have used it over and over for a lot of things where tight final dimensions are not critical.  And you can sand it down after, if you need to adjust more precisely.  I love the stuff.  But be careful!

Please post if you come up with an excellent technique!  I've clearly already disqualified myself...
Title: Re: Weatherproofing Moteino's
Post by: LazyGlen on December 19, 2013, 11:21:01 PM
Yeah, what he said!

Well part of it anyway.

It is hard, rather that soft and rubbery, they claim you can machine it, but I had a hard time getting clean cuts or drilled holes. I may have been trying to work it before it was fully cooled.

I don't see you making motionmote cases out of this stuff. Unless you are a highly skilled sculptor, it's going to look like a 2nd graders fathers day present.  I did get good results pressing it into a mold, and better results when it was closer to cool than hot.

I did notice that at relatively higher temperatures it stuck to other surfaces more. I used water to heat it, and found that some extra care and kneading was necessary to eliminate water and air bubbles.

I did not have the experience of super-heated stick to your hands ouchiness, and will attempt to ensure that it does not happen! My 13 year old daughter loves the stuff, so we use the water bath method.

Instamorph actually sells on their web site a pasta roller that they suggest for making sheets of uniform thickness. I used a rolling pin and bamboo skewers. The way I envision using it would be to roll out a sheet a little more than double the size of a Moteino, poking the antenna wire through and then folding the sheet over the Moteino, pinching the edges closed. (Then cursing when I realize that THIS was the one that I had programmed, the one in the Instamorph only has the node sketch loaded. How does wireless programming work?) Some method for supplying power would also need to pass through the plastic, either wires soldered in or a connector of some sort.

You can "weld" it together by heating it locally and applying pressure, or adding heated material to the joint.

So many things to try, so little time.
LazyGlen
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on December 14, 2015, 06:30:26 PM
Thanks for the posts.  I had never heard of ShapeLock or the other materials before.  Are they non-shrink?  i.e. as it cools, it's not gonna crush or warp whatever is inside it?

Before reading this thread, I was thinking of either using some kind of epoxy (which would probably be expensive?) to fully encapsulate outdoor electronics.  However, maybe plastidip would do the job?  It's not terribly expensive, considering you'd only need a skin of it over whatever it is that you want to encapsulate.

Another idea I've read about is to use a PVC pipe and glueweld PVC caps onto both ends, resulting in what should be a sealed, waterproof enclosure.

What else have folks here tried?
Title: Re: Weatherproofing Moteino's
Post by: Felix on December 15, 2015, 12:36:38 PM
I've used Spraon Clear Electrical Lacquer Sealer EL2000 (http://www.amazon.com/Sprayon-ELECTRICAL-LACQUER-Aerosol-S02000000/dp/B00DRHSFCS)
It's specifically for sealing electronic circuits from moisture and dust. Several coats need to be applied depending how sealed the product has to be.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on December 15, 2015, 02:41:53 PM
Good suggestion!

I just ordered some liquid electrical tape (for some reason, bright green was markedly cheaper: http://www.amazon.com/gp/product/B005FB1VX4?psc=1&redirect=true&ref_=ox_sc_act_image_1&smid=ATVPDKIKX0DER).  The marketing materials describe it as waterproof. 

However, as proven by tyvek, waterproof does not equal vaporproof, and the tech sheet says it does have some small permeability.  I don't know how small is small enough (i.e. what would be a good spec?), so I'm going to do a crude test by applying this green stuff over the electronics inside the enclosures of some cheap solar LED garden lights that my wife recently purchased and which have been rapidly dying one by one from corrosion after just a couple months.  If it manages to halt that debacle in its tracks, then for above-ground use maybe it's good enough, at least where I live.

Epoxy potting material for electronics is probably pretty good, but there's a bewildering array of them, and it's not immediately obvious which ones would be the best choice or the best value for money. For instance, Amazon sells some by 3M, but it costs $17 for a mere 1.7 fluid ounces (http://www.amazon.com/3M-Scotch-Weld-Epoxy-Potting-Compound/dp/B000X5G6O6/ref=sr_1_1?ie=UTF8&qid=1450205932&sr=8-1&keywords=potting+compound).  On the one hand, it seems like a lot for a little, but on the other hand, if it completely protects  a couple  $30 Moteino's  located outdoors from death by corrosion, maybe i't's a smart purchase.  I don't know what the answer is, so anyone and everyone feel free to share your thoughts and ideas.
Title: Re: Weatherproofing Moteino's
Post by: TomWS on December 15, 2015, 03:08:15 PM
I've used Epifanes Spar Varnish (it works well on bright work  ;)  but I don't have enough 'mileage' on my test to draw any conclusions.  Give me another 5 years and I'll let you know.  :)

Tom
Update: Corrected spelling of Epifanes.
Title: Re: Weatherproofing Moteino's
Post by: joelucid on December 15, 2015, 03:55:00 PM
I built a lake thermometer this spring and potted the electronics in epoxy. Worked well so far / but it's only been one season.

(http://i.imgur.com/ebIDSrn.jpg)
(http://i.imgur.com/iLeErHg.jpg)

Joe
Title: Re: Weatherproofing Moteino's
Post by: syrinxtech on December 15, 2015, 04:21:06 PM
That's awesome joe.....you could even add a flag to the lid like the divers use so you wouldn't run over it with a boat.

Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on December 16, 2015, 12:46:55 PM
I built a lake thermometer this spring and potted the electronics in epoxy. Worked well so far / but it's only been one season.


Joe

@joelucid What type of epoxy?

P.S.  Nice photos by the way!  Thank you for posting them.
Title: Re: Weatherproofing Moteino's
Post by: jra on December 16, 2015, 01:41:28 PM
@joelucid like Tom said you might want to apply a coat of spar varnish over the epoxy, especially if it is going to sit in the sun all season.  Epoxy degrades under UV, see http://www.oneoceankayaks.com/Epoxtest.htm for a non-scientific test.  I suspect it won't make a real difference for your application as it looks like your epoxy layer is way thicker than anything I have ever applied to a kayak.
Title: Re: Weatherproofing Moteino's
Post by: joelucid on December 16, 2015, 02:24:27 PM
It's just so pretty, right?  :) :) :)

Made from my youngest daughter's lunch box ... A man changes when living with 3 girls over extended periods of time.
Title: Re: Weatherproofing Moteino's
Post by: syrinxtech on December 16, 2015, 02:45:00 PM
You're preaching to the choir joe....I have 5 sisters.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on December 17, 2015, 12:05:05 AM
FWIW, I did a bit more searching and found that Scotch makes a moisture sealant rubber mastic tape that self seals and is readily available (even my local Home Depot carries it):  http://www.amazon.com/3M-Scotch-Moisture-Sealing-Electrical/dp/B001B1AP3O  At least for one-offs, it looks to be a lot easier, cheaper, and faster than potting compounds.  Indeed, I'm hoping that for basic moisture proofing of a Moteino before slipping it inside something like an outdoor motion detector, it may be sufficient.  Anyone here have experience with it?


Title: Re: Weatherproofing Moteino's
Post by: jarrods on January 04, 2016, 05:24:04 AM
PlastiDip also works great and provides abrasion resistance.

Just remember that any time you are going to try to seal a PCB that you need to heat the board to at least 195 degrees for a minute or 2 and then let it cool to the max temp of the coating your using. If you do not then you will likely get corrosion from trapped water.

Also it is a good idea to clean the board with Acetone first (q-tip not a dunk) to make sure you don't have any flux or other gunk left on the board.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on January 07, 2016, 01:06:44 PM
FWIW, I did a bit more searching and found that Scotch makes a moisture sealant rubber mastic tape that self seals and is readily available (even my local Home Depot carries it):  http://www.amazon.com/3M-Scotch-Moisture-Sealing-Electrical/dp/B001B1AP3O  At least for one-offs, it looks to be a lot easier, cheaper, and faster than potting compounds.  Indeed, I'm hoping that for basic moisture proofing of a Moteino before slipping it inside something like an outdoor motion detector, it may be sufficient.  Anyone here have experience with it?

I tried out this material, and although I did find a use for it elsewhere, I don't think it's the best choice for this application.  Though doubtless it will perform better than regular electrical tape, it does retain some degree of surface stickiness that's kind of annoying.
Title: Re: Weatherproofing Moteino's
Post by: EdM on January 07, 2016, 06:57:53 PM
I've been using heat shrink tubing to form little "bags" around my sensor assemblies, and then filling them with Loctite e-30cl.

https://edwardmallon.wordpress.com/2015/03/01/using-ds18b20-sensors-to-make-a-diy-thermistor-string-pt-1-the-build/

The process is a bit gooey, but once the ends are sealed off, applying more heat tightens up the tube forming a tension structure that makes the final shape very smooth. These have been standing up very well to long term underwater deployments.

(and these cheap dispenser guns work ok:
http://www.ebay.com/itm/221750881004?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT  )
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on January 07, 2016, 09:34:12 PM
Very nice!  I'm guessing that part of the reason you selected Loctite e-30cl was for its low viscosity, so that it would fully encase the wiring without air bubble cavities?  Looks like it may cost around $11 per 1.69 fluid ounce double syringe.  Does that sound about right, or have you found a source that sells it for a lot less?

Great website you have, by the way.   :)
Title: Re: Weatherproofing Moteino's
Post by: EdM on January 07, 2016, 11:27:05 PM
Sounds about right. I usually buy the epoxy from Zoro tools online, and I use clear large diameter poly heat shrink tubing so that I can see if bubbles are trapped before sealing the far end. Sometimes you have to knead the bubbles away from the wiring. E30-CL is a good viscosity for this, but after you (gently!) tighten up the outer sheath, the heat forces the e30 to cure much faster - often hardening within an hour where it would normally take more than a day to do so.

 I usually have lots of cables passing out of both ends but if you don't you could probably seal the ends with small zip ties (perhaps around a small diameter cork?)

Also these are the cheapest mixer nozzles I've found that work OK:
http://www.ebay.com/itm/300933122565?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
(don't buy shorter ones as they don't mix well enough)

Thanks on the site.  My philosophy is that if I can't find something with google, then it's probably worth adding to the blog.  But since I am just learning it as I go along, there's probably allot there to make someone who actually knows what they are doing, cringe.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on January 27, 2016, 01:09:05 PM
Closing the loop: I've tried out the liquid electrical tape, and I'm not a fan of it.  The biggest problem is that when applied, it can bridge voids, but as it dries it gets sucked down into those voids and often leaves openings when it does so.  That necessitates another pass to correct, and sometimes those passes need yet another pass to finally correct.  That, in combination with a long dry time (typically overnight), tallies to a rather lengthy process, unless maybe what you're sealing is a perfectly flat, smooth surface.   About the only positive feature, should you ever need it, is that the rubbery surface that it becomes when it dries is, in some sense, removable without residual presence if you peel it off.

Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on February 21, 2016, 06:11:07 PM
PC Clear epoxy may be a winner:
+ It's relatively cheap ($3.51 for one ounce, including Amazon Prime delivery: http://www.amazon.com/PC-Products-PC-Clear-Adhesive-Syringe/dp/B008DZ19WC/ref=sr_1_1?ie=UTF8&qid=1456094399&sr=8-1&keywords=pc+clear#customerReviews ). 
+ The packaging says not only is it waterproof, it's "impermeable".
+ The packaging says it doesn't shrink
+ The PC Products website says it's non-conductive
+ It claims that it's clear not only in liquid form before curing, but also after it has cured
+ The PC Products website says its nontoxic after curing.
+ It has a 4 minute pot life.
+ It is cured enough within 1 hour that it can be put into service.
+ It comes in a 2-part syringe for easy dispensing. 

[Edit: I've ordered one to kick the tires.  Meanwhile, the liquid electrical tape that I previously applied (above) to a solar garden light's electronics has performed extremely well.  After about a month outdoors, I'm not seeing any of the performance degradation that I had witnessed in the same electronics on a prior occasion when they were unprotected for a month outdoors.  It's still performing "good as new," so to speak.    :)  I'm hoping that the epoxy will perform just as well, but after just one application instead of the multi-pass application I had to do with the liquid electrical tape. ]
Title: Re: Weatherproofing Moteino's
Post by: Felix on February 25, 2016, 04:32:10 PM
WhiteHare, nice, thanks for the update and for your experiments :) they are surely valuable to those looking to put their nodes outdoors or in the ground/water etc.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on March 02, 2016, 03:53:44 PM
You're welcome.   :)

I tried the PC Clear, and I think it would be a good choice for weatherproof potting of a Moteino that's in a container.  For just coating electronics, though, rather than potting them, it's a bit too runny.  It's viscosity is similar to honey.  Also, mixing it in a cup and then pouring it wastes a lot: it's difficult to get it fast enough to where you want it within the time allowed, and a lot sticks to the mixing cup and never leaves it.

So, for those reasons, I'm next going to try their more viscous epoxy, called "SuperEpoxy," which costs about the same and has a longer pot life (15 minutes), but which unfortunately is only  translucent  rather than clear.

Either way, I can already see how gunning it through a mixing nozzle would be preferable: thorough mixing, and you can more easily apply it right where you want it.

By the way, I am curious as to whether hot glue can be used to good effect, as it is definitely cheap.  The most common kind is thermoplastic and waterproof, but I've also read that it can chemically react with the plasticizer used in wire  insulation, causing the waterproofing to fail.  That said, there are different kinds of hot glue, and maybe not all of them are like that.
Title: Re: Weatherproofing Moteino's
Post by: Felix on March 02, 2016, 04:20:40 PM
WhiteHare,
I don't think I mentioned this before, but I like your inquisitive nature and attention to detail, even for such simple things as glue and epoxy. It makes for some really deep and meaty discussions that are sure to be welcome for those that are tech savvy.

Regarding hot glue ... i just tried that on a connector yesterday. I wanted it to be clear so I can see the internal wires colors. While that was mostly achieved, it was a pretty mess in the end and although I didn't do it for weather proofing purposes, I can't help but not want to have to do that again. I'm not that skilled with the hot glue gun and I just created a mess of spider web like hot-glue threads all over my bench and hands and clothes. Messy but... it could have it's niche app for weatherproofing.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on March 09, 2016, 01:38:03 PM
The "super epoxy" worked well in the sense that it stayed exactly where I put it.  At the thickness I was applying it, however, it was much more opaque than translucent.

I also tried the hot glue, and I have to say I like it a lot.  Like the "super epoxy," it stays where I put it.  Dispensing is precise, because it comes out of a hot glue gun, which can be had for $1.  It also rapidly sets and can be put in service within minutes.  Plus, the glue sticks are very cheap (an order of magnitude lower cost than an equivalent volume of epoxy).   Plus, non-toxic, and no mixing issues.  So, I did some test units and put them outside to see how well the encapsulated electronics will weather.  I used some cheap solar lights that I know are prone to rapid corrosion as the test units, so it should flag a moisture penetration problem if one exists.  It will be easy to monitor, because the light won't come on at night or will dim if it fails.  Therefore, how well it performs remains to be seen, but I suspect it will be good enough for above ground, especially if used inside the shell of another container.  Well, time will tell....  I may look into polyurethane hot glue sticks, because those should be thoroughly waterproof if it turns out the cheap glue sticks just aren't good enough.

Yeah, there is spider webbing from the glue sticks, but I found it to be only a minor nuisance.  Also on the negative side, at the thickness I'm using it, it's much more opaque than translucent.  Furthermore, because of possible shrinkage, I don't think I would trust it for an underground (earth contact) installation.  For that, I think I would go with what EdM is using, since it seems that he has proven that particular epoxy really works well even when continually submerged in water.  The PC Clear might work, but its in-use performance is more of an unknown (at least to me), and it might take years for a bad choice to reveal itself as such.

Anyhow, I'm still open to alternate ideas, and I hope others will share whatever they have found works well for them.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on March 09, 2016, 11:01:53 PM
I'm  noticing that encapsulating lithium batteries may be unwise.  That's because many (all?) lithium batteries include venting as one of the safety mechanisms.  However, until now I didn't realize it's true also for primary cells like Energier Ultimate Lithium Batteries.  According to its safety sheet: "Mechanical Containment: If potting or sealing the battery in an airtight or watertight container is required, consult your Energizer Battery Manufacturing, Inc. representative for precautionary suggestions. Do not obstruct safety release vents on batteries. Encapsulation of batteries will not allow cell venting and can cause high pressure rupture."  http://data.energizer.com/PDFs/lithiumirondisulfide_psds.pdf

So, if potting is inadvisable, just how is it that you're supposed to use such batteries outdoors and still avoid their corrosion?  Up until now, I thought they were a great choice for outdoor use, because of their ability to function at freezing temperatures.
Title: Re: Weatherproofing Moteino's
Post by: executivul on March 10, 2016, 04:09:30 AM
All my outdoor units until now have been in small boxes with gaskets, used for food storing, or at least normally found in food hypermarkets (kaufland, lidl).
(http://www.produsecasnice.ro/pics/large/144_540_143_prd.jpg)
Just use the smallest one able to hold what you need since large temperature variances make the air inside expand and contract quite a bit. I can find 10/5/3cm (4"/2"/1.5") in my country for a few pence.
Use a bit of silicone oil on the gasket if you want to be able to open it again or sanitary silicone for a lifetime seal.
The wire hole if one needs it is filled with sanitary silicone as hotglue has a tendency to loose adhesion after a while, and placed on the bottom if the unit is not fully submerged.

Title: Re: Weatherproofing Moteino's
Post by: MrGlasspoole on March 10, 2016, 03:43:54 PM
Hm, the question was weatherproofing but it looks like it turned more into 20,000 Leagues Under the Sea  ;D

I mean there are millions of commercial products for outside usage that are not sealed or maybe just a coat of plastic spray.
Maybe tapplastics.com or Smooth-On has something (Smooth-Cast 300).

What about CorrosionX? You can run motors under water:

There is this spray where they sprayed a 230v hair dryer and did take a shower with him - can't remember the name.
Title: Re: Weatherproofing Moteino's
Post by: perky on March 15, 2016, 08:10:40 PM
Conformal coating might be the answer, but I wonder how the radio modules themselves behave when coated. Does it make the module non-compliant for FCC and CE marking? I think you can get conformal coating specifically for RF stuff though.
Mark.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on March 15, 2016, 09:10:41 PM
As I understand it, CorrsionX is an oil of some type and isn't a "once and done" sort of thing.  It works for RC people because they're hands on and it's easy for them to keep re-applying it.
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on March 28, 2016, 09:33:30 PM
Conformal coating might be the answer, but I wonder how the radio modules themselves behave when coated. Does it make the module non-compliant for FCC and CE marking?

I'm starting to get cold feet on that as well.  I'm preparing some nodes for monitoring our refrigerator and freezer, and I do have that as a lingering doubt about encapsulating them.  Plus the lithium battery "venting" safety issue.   I guess maybe some kind of ip66 or whatever  waterproof enclosure is more of a sure bet.  Maybe include a humidity sensor inside?  I don't know how well or even if it could detect moisture penetration at freezing temperatures, but....
Title: Re: Weatherproofing Moteino's
Post by: TomWS on March 28, 2016, 09:48:18 PM
Plus the lithium battery "venting" safety issue.
Lithium batteries need to vent when you've so overloaded them that they're about to explode.  Your 10uA average current should not be an issue... unless, of course, you happen to exceed that in some, uh, 'accidental' programming error.

Tom
Title: Re: Weatherproofing Moteino's
Post by: WhiteHare on May 01, 2017, 03:34:36 PM
The hot glue method didn't end up preventing corrosion.

It occurs to me now that polyurethane spray foam would probably work 100% and, further, the per use material cost would be a lot cheaper than epoxy.  If you clean out the nozel with acetone after each use, you don't have to use the entire can all at once.  I've done that before, and I've found that the leftover stores quite well.

Of course, it also means your node will be quite well insulated, so you may need to account for that, or possibly monitor the radios temperature so that you don't overheat it.