Do bodywork before priming. But if you don't want to do that... here is what I've used a few times before.... Use a wash primer such as PPG DX1791, followed by K38 high build primer. I've never used epoxy on anything that will be getting filler work... it just makes the primer layers too thick (mils) It is also hard to sand. If I were building a "rat rod" and not worry much about body work or paint then, yes, epoxy would be most durable.
