What type of epoxy primer did you use on body panels? Also, why epoxy mastic in the interior and engine bay? Thought it is more suitable for underside Did it sanded well (for being a mastic)? Maybe I'll be tempted to do the in the interior!
Epoxy mastic primers or epoxy primers should be used anywhere you want corrosion protection, excellent bond to the substrate and or want to seal old paint. I think epoxy mastics have a better substrate bond so there is no reason in my head you'd chose a epoxy primer over a epoxy mastic and a epoxy primer will also be an excellent choice. This is a 1969 Volvo Amazon and I’ve not had a issue painting over with epoxies so it gives a great base for the 2k solid topcoat to go over. I wet on wet so I didn’t need to sand between the epoxy and the topcoat but I wasn’t happy with the orange peel in the engine bay so flatted the topcoat and gave it another couple of coats so it’s nice and flat now. Engine bays and floors are typical areas that get wet and rust in old cars so 100% should have a epoxy barrier in my opinion. How you go about prepping for bodywork and how much you sand the epoxy primer is really down to how you want to do things. Block and fill over epoxy then seal over with epoxy, or 2k high build primer over the epoxy and filling and sealing with 2k primer sealer, or epoxy, polyester primer, sealer, 2k high build primer etc etc.
What brands, types etc has been discussed loads on here but any of the high solids epoxy mastics or epoxy primers from a reputable company will do a good job.
Stripped the fuel tank and epoxy primed it. I also reduced the pressing wrinkles in the ends with my shrinking disc, still no where near perfect but a little better than when it came from the factory. It was more of a play around and a bit of learning to see if it would work. Think I might use my big 2.5mm primer gun to spray the whole tank with Raptor before overcoating it with polyurethane 2k black topcoat.