well etch primer and epoxy dont mix. so if you're going to use and acid etch, stick with that all the way through. but the problem with that also is that body filler isnt compatible with acid etch primer either. so you'd have to go from the etch primier to a urethane primer. the projects im working on at work are in bare metal for a long time, sometimes more than a year, and itd be too much of a pain to keep priming little spots at a time, so what i use is something called Gibbs, its kind of like an oil and silicone free version of wd40. they claim you can paint right over it, but i sure wouldnt try it! but just wipe it down with wax and grease remover, and you'd never know it was ever put on. That way you dont have to worry about priming little areas at a time.