If you want to remove all the corrosion you have to use one of several methods to do so, but there are products on the market that you can apply and paint over, like POR, Eastwoods Rust Converter and Encapsulator or Ospho to name some.
Under normal climate conditions, rust needs moisture and air to grow. Deprive it of one of those and it stops spreading. The problem is that you must completely stop one or both and that may not be as easy as it sounds.
