What do put on bare metal and till drive my car??????????

I need to do a little bodywork to my Dart. It is going to be driven while I am working on it. This is not a daily driver but a weeekend cruiser on sunny days. I have some places that need attention. My question is: what should I use to spray on the places I repair that I have to take all the way down to the metal. Is there some type of sealer primer? I know regular primer is like a sponge when it comes to moisture. What are the options?
I am not going to be stripping the entire car until it is time for paint, just going to do a few places here and there where surface rust is starting to show. I want to get those areas cleaned and sealed until it is time for paint.