Jeff just got the tech sheet on DP epoxy primer. If you are using DP-LF from PPG then you can sand the bare metal with 180 grit sand paper. You have to use a DF body filler "bondo" on top of that because regular bondo will not hold to the DP-LF.
Sorry I am not much help I haven't used epoxy primer since the good old DP 40 days. That was good stuff but bad for the environment and on the body I guess.