I dont know why more ppl dont use brazing to place your metal in holes. It is fairly easy can be done from the underside of any body piece, or actually cut to fit the hole.Brazing flows well and fills well, then all you have to use is spot putty to fill in the space and you dont have a part the is full of bondo. The answer to your question though is bondo does expand and contract with the elements, that is why yours cracked,the metal also has to clean sanded to the skin and I use paint prep cleaning agent made by centari to clean the area well before appling any plastics, which I thourghly despise doing anyway. hope this helps.
Alan
