Another go with new PETG mounting plates didn't yield much.  Maybe there could be separate panels for the power induction on the flat part & the loads on the corrugated part.  Mounting on the corrugated part would still be tricky despite the lack of induction.  Scotch has proven to degrade in the chamber.  The circuit burns 150mA at the USB input.

Welding PETG manely works, but is very brittle & as hard to undo as welded PLA.  It might require a temperature below 300C to avoid boiling off.

Lower starting humidity got it down to -10C dewpoint.  The inductive solution is so obvious now, it's hard to believe it took so long.  The only improvement might be stacking the fan on top of the radio, but it's going to be a miniscule improvement.