Quote: I did not know using bondo was a sin? If the hole is deep enough with enough contours and you think it will stay in there then good. Go with your gut feeling. You treated the metal down in the hole so it should not rust anymore (theoretically). It's your ride do as you wish. My ride may not be perfect to some but I will be the one having some fun. Jay Good luck with your project I know I'll need some.
The trouble is normal body filler is not truly waterproof. Moisture can penetrate it and can cause problems down the road. If you elect to go this route, make sure you use something truly waterproof such as fiberglass matting and resin. Your local autobody store should also have some speciality bodyfillers which are waterproof.
Jay 
Good luck with your project I know I'll need some. 