Cheap sandblaster...(Harbor Freight). Two part epoxy primer. Body filler followed by an 80 grit DA. Auto primer/sealer (beige to tan in color) Follow with thinned spot primer sprayed on...then sand, prime and paint. The epoxy primer is hard like a rock and has very good adhesion properties. Body filler will fill the major pitting and if you want to take it a step further, use the green filler that's much harder than the typical pink filler...more fiberglass. This way there's not as much spot putty needed. The sealer will give you a good idea of how your paint is going to appear and will show areas that need more spot putty sprayed on. Finally, the primer will seal over everything else and give you a good base for your paint. This is how we did it 20 years ago and it hold up very good. There may be more innovative products on the market now but if they're cost prohibitive or dangerous to use you can go this route. Your key is getting all or most of the rust out, neutralizing what you can't get out and putting a hard continuous coating over it to prevent it from coming back through or being exposed to oxygen. Or you could move somewhere that rust is close to non-existant.
