Re Faraday cage. I live in a steel sided and roofed house the panels are not bonded together but yet no cell phone service inside. That was not my question.
When I first got a radio going had rf on the mic. The solution for me was to put an rf choke at the antenna hub. You might consider that solution rather than trying to fight it in the radio.
The finish can be removed pretty easy, too easy from my perspective. Around the case holes it has chipped off on it's own. It looks like powder coating.
_Dave_ AD0B