Just Ospho it wait for 24 hrs, go back over it with soapy water and a scotch brite, and rinse. Dry it out with compressed air, or wait for the rapture while it air drys. Put either magnum steel in the car or use the fiberglass and body filler mix someone mentioned earlier. Smaller spots i'd go with the magnum shit. Just sand that down and primer it before condensation get on it. Definately don't Ospho and let sit. You paint over/after the Ospho within 48 hrs, but ideally before condensation gets on it. I.E. don't let the car sit in the elements over night.