Yeah I have a MobiArc welder on my truck. I use it for stick and MIG with a spool gun. Flux core of course, I draw the line at hauling gas.
It comes in real handy and I don't have to haul as much beer on trail runs since there is always someone with something busted that needs welding. They are always grateful and will provide lots of beer when they are on their way again. I've lost count of the Jeep tie rods I've welded on the trail, there always seems to be one of em out there somewhere with one wheel going one way and the other headed in another direction.
There are three or four underhood welders on the market. I chose the MobiArc because it's smaller and more efficient than the others. I did have to modify my alternator but it was not a big deal. The welder becomes the voltage regulator for the truck. When you touch off welding, it automatically disconnects the alternator from the battery then runs the alternator voltage all the way up to about 36V and the truck runs on battery power. When you finish welding, about 15 seconds later it automatically switches back over. A hand throttle is used to control welding power, more RPM provides more power and penetration.
You can also pull and use a couple of batteries in series with a spool gun or stick. It isn't always pretty but anything to get you off the trial because AAA ain't commin, even coat hanger wire if it's all ya got. LOL