you can use a good body filler it will work just fine and would be better to work with or a glass filler. i like to use the tig with 1/6steel filler rod or a mig set cool just to fill in the pits and hit it with 36 grit and go to 60 grit with angle grinder then up to 80 to 120 on a da at this point done you will not have much at all to fill less the frame is very pitted