I totally agree with Bubba.
A good quality paint job will do exactly what he says.
Any rust at all is like a cancer. You have to get rid of it all or it comes back.
The other trick, if you want to stop it from progressing, is to isolate it from oxygen.
There are 3 things that are required for corrosion to happen.
An electrolite.....like water or humidity in the air.
Disimilar metals that contact each other via the electrolite and create an electrical potential (anode and cathode)......rust is a disimilar form of metal.
One great product that will Paint Over Rust is POR 15. It will seal it from both oxygen and water........if you don't want to go the sandblasting or welding metal route.