if it's bubbling from the inside out, the rust has already eaten from the inside wheel well out, so just sandblasting it and repainting isn't going to fix the rust. a few more months and it will penetrate back through. the only way to eliminate the rust entirely is to cut out the rusted area and weld in a new piece. I didn't care if it came back, so I just did a kick ass bondo job after cleaning it all up. doesn't look perfect but a whole hell of a lot better. Mine was completely rusted through on both wells.