Are you talking about the water proof bondo called "all metal"? I have tried that years ago and it didn't work out. The right way is to weld in metal where the holes are. Anything other than that will not last. Use a bucket of water, some water soaked rags and weld a very small section at a time. That should minimize the distorting. Heat is what causes the warp, so try to go slow and keep as cool as possible. Someone even makes a putty heat sink material you can place on the roof skin. It will keep the heat from transmitting. Good Luck!