37lookin,
I'm not sure if this is what you had in mind, but this would be my recipe..strip, grind, or sandblast the item (dented) to a clean bright finish. Apply two part etch primer followed by 2 part epoxy primer. Now you have the ability to work on the dents and bangs at your leisure OVER the 2k primer.
I don't think you need to do anymore surface prep before body filler other than a little roughing of the surface.
This method might sound funky, but I think it is SOP these days in body shops. Ideally, the primer substrate is bonded with the sheet metal, and anything applied to it is for keeps!
The paint you saw on the rig in the body shop was probably 2k primer. There has been tons of banter in this forum on this subject. I hope this unprofessional information helps answer your question.
Stuart
