Im molding in some gauge pods into a spare A-pillar I got, and I was wondering what kind of filler or bondo I should use for the plastics. I know its probably easier to just buy a gauge pillar but I want to take this project on myself and make it custom. I'll either be wrapping it with vinyl or spraying it black when its done being molded.

 

I would suggest using fiberglass instead of trying to mold any of that with Bondo. Unless I'm misunderstanding your intention.

 

+1 bondo is for finishing touches.

 

I've used a product called bondo glass with great results on plastic. So far, my parts are at least 5 years old with no cracking and are in great shape.