I decided to move my 8-watt APRS transmitter to my car and install a smaller, lighter, 300 mW one in my plane. I bought a Micro-Trak MT-300 and today I installed it in a plastic case, similar to the previous installation. This one is actually better, because I soldered the 9-pin serial connector directly to the printed circuit board. This greatly decreases the number of soldered connections in the system, which is good for reliability.
Both the APRS itself and the regulated 12V power supply are mounted on standoffs. I'll complete the rest of the wiring soon.
[Superseded.]