With respect to the failure of my paint (above - can run fingernail down to bare metal), I may have been able to prep better. I work in the office of a plant that punches and bends sheet steel and aluminum. The piece I used was scrap new stock. When I took it home, it had the protective oily residue from the factory still on it. I sanded the metal with 120 and liberally doused and wiped with mineral spirits before my first coat. What more should I do to cut the residue? I still have the other side of it I would like to test with.

I'm curious how the paint will react to the project I want to paint with it (fiberglass dune buggy). I would think that fiberglass would be a little 'thirstier' than sheet metal.