Buy a name brand MIG with gas capability and be done with it--it might cost more,but its worth it,and a 220V one is much better than a 100V,though some of the better 110V MIG's do well on thinner metal..
--sheet metal sucks to weld with anything else except a TIG torch maybe,the flux core welders are usually not DC in the cheaper models and are NOT a MIG,they are wire feed arc welders,and they blow holes in sheet metal just as fast and too easily just like a stick welder will...
Even a DC flux core 110V welder will not be easy to use on sheet metal with success...
After using a real MIG that runs on 220V,I was able to make continuous beads like a pro on thin body panels,I had borrowed both a wire feed DC 110V welder and a Harbor Freight 90 amp wire feed AC arc welder and succeeded only in blowing holes and getting so pissed I wanted nothing to do with welding sheet metal...going to the 220V MIG with CO2 & Argon made a 100% improvement..
I only wish I could justify owning a 220V MIG,I do not use one often enough in my case to justify the expense,and it is unlikely I'll be doing much more body or rust repair in the future (if I can help it)..unless I stumble across a deal on one I will be unlikely to buy one..I've managed to get by with a stick welder and brazing things but its not the greatest way to weld thin stuff..