Just use epoxy chassis paint,all in one step. The factory never primed chassis parts. Only the firewall was primed with the body shell,and I don't know about the radiator support or fender wells. I used epoxy primer followed by single stage BASF urethane on my Fire bird and it was still too soft. Regular enamel or laquer will be too soft to hold up. You have to remember that the factory finishes didn't last long. I would go with the strongest epoxy you can find. I haven't tried that ceramic infused stuff,but it is supposed to be good. Power coating would be even better if you can swing it. My dragster chassis was powder coated and it was tough as nails.