primer

PPG has a line called Shopline. On regular jobs I use it since it is around $50 a gallon with the hardener. If you have any bare metal you will need to apply a light coat of acid etch primer for adhesion purposes.

If you don't use acid etch then you need to use an epoxy primer like DP90LF that bonds to bare metal without the acid etch. Its PRICEY though. You can get acid etch in rattle cans. Be sure you only apply the acid etch to bare metal only, not your filler.