i hate to be negative, but i think you should use something a little heavier than what your using, take your time and make it fit perfect, remove ALL the rust and paint any bare metal before you start putting more metal in, you can get shaped patch panels pretty cheap at body shops, if not pick up a peice of 20 or 22 gauge sheet metal and start with that, it will be worth it when your truck is still one peice 10 years from now, if your not going to weld it in, invest into a decent rivet gun and use rivets, they will finish it off alot better and they wont back out on a rough road, keep plugging away and learn as you go, with your determination and ability and a little help and advice you will have one nice truck at the end.
Jon
Jon