Is this just a bit of mild surface rust or are there bubbles in the paint with rust holes? If it is just minor pitting with the metal still quite solid, then wire brushing paint rust off etc, then applying rust converter (let it dry and wipe off residue - see instructions on bottle), then applying something like killrust is quite adequate. To match the paint the steps would be, same as above but instead of killrust (or whatever), you would clean with wax/grease remover, apply etch primer, apply putty if necessary, sand, apply primer/high build primer most likely, sand then paint top coat colour.
If there are holes then no rust converter/sealer will help - it will mean having it cut out and replaced with fresh metal. Don't be tempted to bog it up, there are far too many bodged repairs out there already.