I took my parts to a guy that all he did was automotive sheet metal - he used ground glass as a medium. Like others have said, you really want someone who knows what the hell they're doing or you'll have a real mess on your hands.
I talked to soda and plastic media strippers too, but the problem with soda/plastic is it really won't touch the rusty spots, just take the old paint off.
I tried the caustic bath treatment on a couple of doors, but in the end I had them glass blasted too.
The same day all the sheet metal was done at the blasters, I took it home and sprayed it with Southern Polyurethane's epoxy primer. Acid etch primers make me nervous and this product gets the job done well.
https://www.southernpolyurethanes.com/primers