A couple flavors for your portable welder. Qman has a trick setup under the bonnet. Seen the same setup on a Toy Land Cruiser last week. Definatly a good way to go.
Toyota duder also had one that clamps onto a battery and wire feeds for some welding action. He couldnt find it at the moment so I didnt get to check it out closely. He just explained it's basics.
Anyway their are some neat portable welding options for seriouse offroaders. There's also the shade tree's battery welder buuuut I really dont understand how that works properly and it really didnt sound too safe :-p And that's all I have to say about thaaat....
We also have the hand held wire feed attachment. This is a pic that shows the welder(blue box), dual battery set up, under hood lights, relay block for the off-road lights and the winch wiring from the drycell battery.