epoxy paint ?'s

Most epoxy primers I have used are non sanding... they sand like bubble gum. Lots of people suggest "sandwiching" your body filler in epoxy primer... bare metal covered with epoxy, bodyfiller, epoxy primer. Never made much sense to me as a body man.. First you spray the panel with epoxy... let it dry, then to get the filler to stick you have to sand epoxy. By the time you are done doing your filler work you will have most of the epoxy sanded off in my opinion. Seem's like a good concept for rust but not very user friendly. I would suggest doing your bodywork and finishing with a coat of epoxy, or a good corrosion resistant primer such as PPG Ncp170