[HardcoreZ28]

If it is more than just surface rust then you want to cut the section out with a cutoff wheel, make a new piece out of sheet metal...try to mold it to the same shape as your original. Tack it in with a MIG welder....then slowly weld it solid so you don't warp the hell out of it. Then grind your welds, skim with body filler, sand, prime, paint.