There’s no need to buy a new Tig machine for welding sheet metal … I’ve been using my 300 dollar Ideal Arc at home for 15 years … there’s just no moving it around.
I have a high dollar Miller Dynasty at work and can see no advantage when it comes to welding sheet metal.
Mig’s
Use small - soft wire
Use consecutive tacks
Back any gaps with copper - brass - or even aluminum
When you blow threw
Quick pulls on the trigger you can deposit a drop on one side then the other to get a new start.