Home depot sells some nice Phosphoric Acid. It'll take off any rust anywhere with minimal scrubbing in. Then you have to sand, prime, sand, paint, clear coat, wetsand and the rust won't come back. If you leave even 1 molecule of rust, the rust WILL come back. Those 'rust killers' that you spray on are mostly bullshit. Be careful with the Phosphoric acid, though. Repeated uses will take off your paint, and then turn your metal funny colors. Its powerful shit, and to be used with care.