Really. Rust is rust, is rust. Needs to be cut out and replaced with new metal. No real shortcuts. Take dremel with cutting wheel (angle grinder with cutting wheel for larger sections)...cut out rusted area to clean metal. Cut sheet metal to fit these areas and weld in. If new to welding...get lincoln or similar 110v wire feed mig welder and follow wire size, feed speed, heat settings for thickness of steel you're working with. Do some practice pieces. Craigslist or harbor freight can offer great bargains on start up set (cl sellers will often give ya lots of extras with welder like helmet dollies clamps etc. Tip to not warp things out: "stitch weld" sheet metal. Lots of small spot welds with cooling time between sections. Move around a lot...don't try to do in one bead. When patch is good, grind welds down smoother. Little bondo skim... sand, prime, paint. Remember, cant weld dirty or painted metal. You'll need to grind weld areas to shiny metal. A tool and skills that you'll use for a lifetime on countless projects!
