IMO....Im not sure painting over rust is a good idea either. Once rust starts the only way to stop it is to wire brush it down to bare metal, and cover it with a NON- drying product like fluid film or similar. I personally use "Rust Check coat and protect" that come in a green spray can from Canadian tire. Dealers are putting a rubber based rust protector on from the factory that drys, and this is the worst stuff you can put on your frame. Once is cracks ( and it will happen) it traps moisture in and rust will form and spread like wild-fire because is never gets a chance to dry out. I seen it first hand on my old 2002 s-10 which i purchaced second hand with 80,000kms on it, and underneath the rubber undercoating was scales of rust the length of the frame.