Also remember that if you shoot it with primer or any flat or satin paint that is not a SEALER, you may as well cover it with a rag soaked in salty water. Primers (and body filler) do not stop moisture, that is why rust is creeping through. If you are going for a primered (rat) look, paint it with a sealer, or a gloss color first, then go over it with a flat, that will give you the primer look with rust protection.
