Best epoxy primer

I think the theory is that body filler is porous and can absorb water. The epoxy layer protects the bare metal if moisture gets below the paint and into the filler.

I used SPI Epoxy primer. I loved it. I've read the Dupont epoxy will plug your sand paper. But you could block sand the SPI if you wanted to - no problem.

They say you can apply filler directly over the epoxy without scuffing anytime within the 7 day re-coat window, but I scuffed mine just to be safe. I also used red oxide epoxy and gray primer surfacer. That way I could tell when I had sanded down to the epoxy and avoid going all the way to bare metal.