please help, my car has a hole in it

:shakehead my 82 grand prix has a hole in it, whats the best way to fix it? ive bought Bondo, FiberGlass Mat/resin liquid stuff (how do i use that?? no instructions), and some metal Tap. :uhoh:

o ya and heres a pic to show you the hole. The hole is a bit larger now and i can get to the other side of it in the trunk

http://www.nitroextreme.com/cars_trucks/nitroextremepark/message_board/albums/58/2.jpg

Rust is like cancer, chances are its gonna come back. The best way to fix that would be to replace the rocker panel. Next choice cut out all the rust & weld in a new piece a metal.