[Daves55Sedan]

The idea of using the copper spoon is excellent, but since I don't have one, I usually cutout a strip from the sheetmetal scrap pile. Cut to lengths to fit each side of the new metal piece and tack weld the strips to the back of the new piece such that the strips stick out a little bit. This will only work if you can slip the new piece in from behind and wedge it into place with tools and wood blocks or something. The thin strips prevent the mig welding wire from slipping in between the new and hole in the old panel and helps to prevent burn through.