Rust is one of the worst things you can get in a car, but there is a way to get rid of it without having to go all out and do some major reconstruction to your vehicle. You can use Rust-Oleum Rust Reformer Spray.
This spray is meant to be used on top of a rusted area and then you can sand it down and paint over it. Whereas rust will usually make its way through the paint, you can use Rust-Oleum Rust Reformer Spray to create a paintable surface.
Buy it right here: Rust-Oleum, Black, 248658 Rust Reformer Spray, 10.25 oz, 10.25-Ounce $6.27