Years ago Hensley Battery in Denver made one like the Premier Power welder and it worked great. I watched a guy run 1/8" 7018 as smooth as silk. His even had high frequency. I think Hensley was the innovator for that type of welder. They rewound a Delco alternator. Craig

 

I have the MOBI-ARC welder on my Blazer and LOVE it!!! Capable of 200 amps, small unit, runs off the alternator only. Digitally controlled, when you strike an arc it senses that and isolates your batteries and runs off the alternator. When you are done runnin a bead, it waits 45 seconds or so before charging the batts again. Used it lots, for around the garage as well as on the trail. It's a hi-frequency unit, so when welding it sounds like the rod is screaming!! You do have to either modify your factory alternator with different diodes or buy one of theirs. Cost me around $800 bucks or so about 4 years ago. Put in a pic, if need more let me know.

 

We use inverter welders on our service trucks. I have a Miller TIG inverter on my '05 that weighs 10#, runs off of 115-230VAC, and is rated at 140A max.