1. Scrape old undercoating off with putty knife
2. Remove residue with solvent
3. Scour with SOS pads. (I like using them for this as you get the combination of soap and steel wool. Leaves a nice clean, smooth surface.)
4. Treat with TSP, rinse with water, let air dry in warm sunshine
5. Coat with Rustoleum's trusty, rusty metal primer
6. Top coat with Rustoleum's Truck Bed Liner
Got the second fender top coated just as the sun ducked behind the hilltops and the temps dropped 10 deg. Nice to get that job done outside as the bed liner contains Xylene which is some really nasty stuff for working with indoors.
Once I get the inner splash shields in place, I should be ready to mount the fenders. At that point she should start looking like a car again rather than a 20 year long high school science project.
So for the quiz. Anyone wants to guess why there isn't an antenna hole in the top of the passenger fender? You'll be surprised by the answer. And no, I didn't weld it shut.