Martinsr,I have been using just PPG epoxy over prepped bare steel(sanded well with 80 grit),then filler,2K primer,and then color.I must say I'm really sold on the epoxy.I haven't done any body panels using this yet,just chassis and engine(no 2K on the engine)but I did do a pedal car for my daughter about 3 years ago and finished it with Concept single stage and it has held up beautifully.Even where the neighbor kid decided to whack it with a hammer a few times.
My reason for asking was that a couple of coats of the epoxy adds quite a bit more to the overall thickness of the paint than I assume the wash or etch. I haven't tried either of them so I can't say how they'd work. I can say that epoxy really seems to stick though.
