Hi Alix,
I almost missed Tom's reply.
+1 for all his comments.
I also noticed on the datasheet that you may need additional components to make it work properly.
Were you going to add another PC-board with this antenna on it?
John
I think the additional components are the matching network that may already be on the RFM69 board. Assuming you don't totally detune the antenna with your layout then you may not need these.
Suffice it to say, ANY implementation in an enclosure smaller than the ideal is going to affect performance. The good news is that the RFM69 has a lot of 'room' to spare in this department and, as long as you're not trying to get 100s of meters of range, it just may be good enough, especially since it's ceramic.
Tom