Find a friend with a mig welder. Do it once, do it right. Grind it back til you get to solid metal. Overlay wide strips of tape over the hole, mark the contours and use as a template to cut a patch, then truck over to your friend with the mig. Grind back the welds, use some fiberglass bondo for the deep stuff, regular bondo for the light stuff. Sand til you get sick of doing it (get it flat and smooth), hit it with primer to see the high spots, sand some more. Prime and paint.