The area you are working on in the thumbnail is the same area I have rot.
The welder is a Lincoln Electric. Tried it yesterday, seemed pretty good, clean weld and fast.
My concern (and at the risk of sounding stupid) is after joining two pieces of panel, how does one grind smooth the weld without "digging" into the panel itself? You can't hold a grinding wheel "flat" against the weld; it's going to be at some angle???
Should you weld from the "good" side or the back of the pieces???