A couple of major changes to the project.
1. After fighting with the Moteino, the keypad and the Nextion (mainly due to the one serial port) on the command/control box, I ditched the Moteino and went with an ESP32 with an external RFM69 radio. This also meant pitching LoRA, which I was OK with seeing as how most of the gains in LoRA distance would be negated by the trees and terrain. If I was using this in a drone or balloon which is mainly vertical, I would have definitely kept the LoRA. I know there are ways to work around the one serial problem, and I have done it on other projects, but after spending 2 days banging my head I decided to cut my losses and switch to the ESP32. This change also gives me Internet access via wireless which I can use to stream log messages to the Internet for analysis and storage. It also gives me BT in case I want to work on a phone app. I had to remember how to handle the packing of the structs between the Mega and the ESP32, but I was able to get everything working.
2. The Nextion UI is almost done. I have added all the necessary code to enter the 3-digit command into the keypad, send the command to the rover, and accept the log/data output and display it on the Nextion. I'm thinking about taking on a scrolling window which would allow me to view older messages.
3. I need to wire up a HW radio instead of the W model I have now.
4. Still need to finish the fan circuit and finish testing.