I just looked up the Lenco spotweld mark2 L-4000. I wish I had run across this about 10 years ago when I was welding the panels on the Roadrunner!!! Not cheap but when you are doing close to a 1000 spot welds, it pays for itself. The time savings alone would justify this machine over using plug welds. Looks like there are two electrodes. One does the actual spot weld and the other is a ground of sorts on the back side and doesn't have to be on the same spot as the spot weld.