Thanks for the input.
Perhaps going with a linear power supply would be the way to go, I did
not as there are already three switching DC-DC power supplies on the
MB, the power efficiency is less than 50% for linear and I would have
to deal with the heat issues. I could just string a bunch of LM78xx and
LM79xx to get the required positive and negative voltages.

I've created a seperate smaller case for the PSU as creating a new
single case would have taken longer and I don't know about what level
of cooling issues I will have. I've noticed the PSU manufacturer (not
surprisingly) has reducd the MTBF when it is in hotter conditions. (but
hey perhaps I could use the heat to warm my cold toes in the Long Ez)
If the weather clears tomorrow I will go flying and measure how much of
a problem I have with it operating.

Thanks for the continuing input.