Most EVs have a very normal-looking 12-volt electrical system for the instruments and accessories, and then the HV traction battery is treated like a fuel tank, with the HV contactor switched on and off like the fuel pump, more or less. Then a DC-DC converter takes the place of the alternator, to keep the 12v side powered.
Is the Aptera like this? I'd like to understand its suitability for ham radio installation, since on paper, it looks absolutely ideal. (Hopefully said DC-DC is nice and RF-quiet!)
Yes, there's a 12V system*, so your final statement about RF-silence could be the real question, assuming a ham radio doesn't take more than the converter will supply.
*Line 3 of Aptera's FAQ Spreadsheet , searchable by Ctrl+F (for "Find") or cmd+F for Mac.