I would agree that needing to weld more than 1/4" material on the van is rare. You can build some really strong boxed stuff out of 1/4". Some of the "200ish Amp" inverter welders will go up to 3/8" which is thicker than anything my 10,000 lbs hitch is made of.
The scrap metal yard that I get my materials from is kind of huge, and ever piece looks smaller there than it really is. Every time I find myself struggling to move some stock, I have to remind myself that it's a van and not a tank, and that I should look for something smaller.
While I generally use TIG on all the little stuff, because making room to make a mess takes me time, and nicer welds are well, nicer. It's also nice to have a MIG gun to blast through a bunch of welds on projects that require that.
I've been eyeing plasma cutters lately. In reality, I want a mill, but a plasma cutter doesn't weigh as much as a mill....
'99 EB ex ENG KSWB news van, low rent 4x4 conversion (mostly fixed by now), home built interior.