I bought a cheap MIG welder at Canadian tire and started practicing on sheet metal the trick is to take your time because sheet metal gets very hot, so I tac wait 1min another tac wait 1min etc and for me it worked great. And the grind the weld even if its not perfect looking u can still grind it in the end. Oh and buy splatter sheild spray if you dont get a gas with the MIG. I have a home made spot welder made with a microwave PSU works wonders on sheet metal wear you can reach both sides. Good luck.