I epoxy primered first, then build primer, then filler, the build primer.
I used PPG DPLF expoxy primer, K66 build primer, and DCC acrylic urethane topcoat. The reason I did build primer after the expoxy primer is twofold. First, the epoxy primer must be coated within 7 days of application in order to work properly (according to the tech sheets). Secondly, when sanding down my filler, I only sanded into the build primer, leaving the epoxy primer intact to seal the metal. (Use different color epoxy & build primers to help this)
