I built a test linear regulator power supply this evening and the TO-3
regulator bringing ~12v down to 3.3 Volts nearly burnt a hole in the
test board. I looked over the wiring which was OK so it looks like the
thermal output of bringing 12volts down to 3.3 for 3 amps is just way
too high. So so much for that idea (unless I am missing something)

I may just end up getting on the EPIA TC models as UltraJohn mentioned
and hope that their EMI/RFI solution is better. The plane battery
voltage is ~12volts idle and ~14 volts running, what is a way of doing
the "power stabilizing" necessary for the EPIA TC which requires
11.6-12.4 Volts? If I just put a 12V linear regulator on there the drop
off in voltage would prevent the system running off battery.