I have a 39 chevy street rod project underway. The body is stripped to bare metal, top chop complete, and ready for leveling of all the welded seams and a little re-contouring here and there. There seems to be differing opinions as to whether to apply filler at the bare metal stage or prime first with a metal etching or epoxy type primer and then apply the filler. I have not done any filler work since the days when "bondo" was the only product around. Which is the currently recommended procedure and what products work best in this application?