Any kind of welder can be used but the best results come from a competent repairman using a tig or mig welding machine.
Welding pin holes in sheet metal.
The most permanent repair to a hole in sheet metal is to weld the hole shut.
Mix the epoxy and apply it to the front side of the backer and the center pin.
I ve read that works for welding shut drilled holes.
I ve done some gas welding with varing degrees of success.
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The complexity of welding increases as the thickness of the material decreases.
Try going for a wire of 023 inches when welding sheet metal.
Immediately after applying the epoxy to the backer you can insert it in the hole and pull it up until it is tight with the original panel and slide the retainer clip over the pin until it touches the metal and firmly holds the backer in place.
I have no experience with mig other than reading various forums.
My thought for the pin holes was to back them up with sheet copper will running a bead to help prevent blowing through.
I ve soldered all my life.
The welding process actually adds new steel to the thin steel and can result in a repaired spot that is stronger than the original metal.