The real down and dirty way to fix it good enough for inspection or to get by for a short time?My trick is to use Marglass or similar fiberglass reinforced filler-grind about 1-2" around the area, mix up enough to cover the hole and ground area, layout some 2" tape sticky side up using rows overlapping to cover the area plus 3-4", blob the mixed Marglass onto the sticky side of the tape, pickup the tape and smoosh it into the hole roughly smoothing the tape to the contour of the body.Wait till the Marglass harderns, peel off the tape and if you want to get pretty grind/sand it down smooth and prime and paint.Of course you may need a couple more skim coats to fill in any voids.Cheap, quick and easy but obviuosly a total hack job but works in a pinch!