I'm no expert, but I used Omni epoxy primer over bare metal. It sticks good, seals the metal to prevent rust, and in some places I used some filler over the epoxy with no troubles. It's a medium cost primer, there are probably better more expensive epoxy primers out there. It's not really a primer you will be able to sand much, it gets pretty hard. You can read the spec's for it online, or just google it.
If you aren't going to paint over it right away you will probably need to scratch coat it before you cover it with primer/paint later.
I also used a high build primer in areas that had some pitting, sanded down to fill the pits.
