overlander
Expedition Leader
For stick welding Al E4043, reverse polarity (electrode positive).
If you're thinking a Land Rover body panel E3003 might work better, but using batteries would probably be too hot for something that thin.
I can't think of a circumstance requiring a body panel to need to be welded to get out of the field and back home. For that, I would say carry a small piece of sheet aluminum, a hand drill, tin snips and a rivet gun with some aluminum rivets of various lengths.
"Getting back home" welding is chassis, SUSPENSION and power train!