a guy i work with says that the best thing to do after stripping old paint and bondo down to the bare metal is to rub it down with vinegar and then use a primer called k201. anybody ever hear of doing that?
You want to look for a "self-etching" epoxy primer for painting bare metal. The etching component will prepare the metal surface for maximum adhesion....and the epoxy part means that it won't absorb moisture (leading to rust) the way regular primers can. Just my $.02 Dickson