I originally bought a Hobart flux core welder it did nothing but blow holes thru. When I called Hobart they suggested holding the tip about 1/2 inch away, I don't have that kind of control. I sold that and went out and bought a Miller 140 with auto-set. They don't make that model anymore but I'm happy with it... It wasn't until I read a bunch and watched a lot of videos that I realized that you don't want to do long beads on butted sheet metal. If you are lucky enough to run a bead it will warp the metal. For my purposes doing many many tack welds jumping around from one point to another has kept the metal from too much warping. or at the link above calls it "Welding sheet metal with a Mig involves what I refer to as "dot" welding. One zap at a time." You end up having to do a lot of grinding... I generally use my 4 inch angle grinder and do touch-ups with my Dremel grinding wheel. I don't know why they only sell 2 Dremel grinding wheels at a time.

My 1950 Chevy 1/2 ton blog