Hence my dream to move as much as possible out of there.
Icom/Kenwood/etc make 2mtr ARS/VHF commercial radios with a detachable
~0.5" thick panel, and simple connecting cable.

I'd make it a fiber, and move the bigger boxes to under the rear seat
where cooling and access are both easy. Little box with mike/earphone
jacks going back there.

Not exactly a new idea. Most WWII aircraft radios had a control box
and a remotely-mounted main chassis. My first airplane had a Narco
Omnigator "coffee grinder" with that arrangement. The remote part too
up a fair percentage of the baggage compartment. It sort of worked,
but you had to speed up the engine (and stand on the brakes) on the
ground so the generator would kick in and bring the voltage up to
where the transmitter would work. I don't miss it. BTW: it had vacuum
tubes and a vibrator power supply. Anyone remember those?

David Johnson