most of the time removing the rust and spraying will do nothing.
This is coming from one of my friends that's done autobody/paiting all his life.
The problem with spray cans is the paint in them is not waterproof, water can get right under the paint and into the rust underneith (basically the paint is there, but its not really there). The only way for sure to remove rust is a good urethane primer, This is waterproof. Rust inhibitors are a waste of time/money IMO.
