I had an Ex-Auto body shop Owner at my home assessing some hail damage on my Caravan. He had a Street-rod T-0shirt on and my '53 1/2ton was sitting in the driveway so we got into the inevitable discussion on cars and trucks. He told me he had Restored or created over 300 units in his over 25 yr. career in the body Biz! Sounded like he really knew his stuff. The discussion topic turned to rust and POR 15 and he told me about Lord Fusor. I'd never heard of it, but he told me definately NOT to weld any patch panels, but rather use the Fusor 2 part epoxy to fuse the panles in place. He said they are completely heat resistent and work fantastic. His only word of caution was that you'd better get your panels in the right place the first time around...cuz they ain't movin' once they cure! Here's the Lord website link. Check it out and see what you think. I will give it a try.
http://www.lord.com/products-and-solutions/adhesives/automotive-repair-adhesives/product.xml/289