If you don't want to go to primer right away while you do body work, one option I like is to coat the bare metal with Picklex 20. It is a metal prep solution that leaves a temporary protective coating against flash rust as long as it is kept dry. You don't need to neutralize it or rinse it with water like some metal prep formulations. When ready to paint, I just scuff it and spray epoxy primer right over the Piclex as it acts as an adhesion promoter for the primer. You can buy it direct from the manufacturer (do a google search) or I think autobodystore.com sells it too. It's a bit expensive but goes a long ways from my experience.
-Ed
