Bodymans tape?
I use clecos but you can use sheet metal screws as well to hold the replacement panel tight to the original panel. Then I take a thin cutting wheel on my angle grinder and slice through both panels where I want to weld them. I tack the two as a butt weld, then switch to a saws-all and cut a little more and tack, and so on and so forth. On the back side a strip of waste will eventually be removed as well as on the front. Kind of like cutting a wallpaper seam. Then I go back and fill in the tacks between the first tacks, only welding a 1/4 inch at a time and keeping it cool. Eventually it is all welded up and you can then grind it flat on the outside. The picture is prior to cutting and welding but fitted up with clecos. I use .23" E70-S wire at about 17V and around 300 inches per minute feed. You will want to look at the back side of the weld and be sure the base metal is totally consumed (no cut edges showing at welds). The metal on the back side should be proud of the base metal. If the back side looks good and is flush to proud, then you can grind the front side flush. Keep the metal cool when welding and grinding by moving around.
I have some photos of the rear side and one of the front but they are on my phone and kind of a pain to move over.
I use clecos but you can use sheet metal screws as well to hold the replacement panel tight to the original panel. Then I take a thin cutting wheel on my angle grinder and slice through both panels where I want to weld them. I tack the two as a butt weld, then switch to a saws-all and cut a little more and tack, and so on and so forth. On the back side a strip of waste will eventually be removed as well as on the front. Kind of like cutting a wallpaper seam. Then I go back and fill in the tacks between the first tacks, only welding a 1/4 inch at a time and keeping it cool. Eventually it is all welded up and you can then grind it flat on the outside. The picture is prior to cutting and welding but fitted up with clecos. I use .23" E70-S wire at about 17V and around 300 inches per minute feed. You will want to look at the back side of the weld and be sure the base metal is totally consumed (no cut edges showing at welds). The metal on the back side should be proud of the base metal. If the back side looks good and is flush to proud, then you can grind the front side flush. Keep the metal cool when welding and grinding by moving around.
I have some photos of the rear side and one of the front but they are on my phone and kind of a pain to move over.