I'm gonna make an unusual reccomendation. Firstly though, I've used Por 15 many times and my main gripe is that it is really picky about surface preparation and even when you do everything they reccomend the results are sometimes frustrating. That said, Rustoleum has served me well. You can spray it by reducing about 20% and it flows really nicely. Give it several weeks to cure and it is really durable. Anyway, consider a product that is readily available and easy to use before you use some of the specialty paints. Another to consider is PPG's DP 90, an epoxy primer that is super durable and looks great on chassis because of it's low gloss finish.
Joe
