My first welding job I started in a stainless shop and all we used were miller tigs and this was on 16 to 20 gauge stainless.We built restaurant packages for Red Lobster,Olive Garden,Zio's,Sonic and others.We built large tables and salad bars and it couldn't be warped all to hell when you were done so fitting,the use of cooling bars,wet rags and the ability to control your heat was very important.When fitting sheetmetal both parts need to be flush because if you have any gaps it's going to pull when welded and you need tacks every 1/4".We flashtacked everything and to do this you set the machine on 150 amps and at a 100% then with no hood on just turn your head and quickly stab the pedal and let off and after getting used to it you can vary the size of the tacks plus move along quickly.I'm wanting to try this on my car's sheetmetal and just flashtack the whole seam moving around and using a wet rag until it's all sealed and there shouldn't be hardly any heat in the panel and hardly any warpage.If you're going to try to weld a 1/2" at a time use a wet rag and move around plus weld into another weld instead of starting at the end of a weld then stopping this keeps it from pulling as much.Also thin sheetmetal is easily penetrated so run small and narrow beads and travel quickly with your torch and as soon as you lift up slap a wet rag on it.We mainly used 1/16 tungsten and water cooled torches.
I didn't learn any of this in welding school.I learned it from guys in this stainless shop who had been doing it for 30 to 40 years.I found out quickly what they called "shop experience".

Brian