For what its worth, I have a century 125 gl 'home' 110v rig. 4 heat settings, variable wire speed, no gas tank.
Follow my links, I have welded together a big flatbed (also in the build a bed section) and welded together all kinds of stuff with it. Its also welded in my shock mounts, on both frame and rear axle, and my engine mounts for my 292.
My flatbed has carried 3000+ lbs of scrap on a few occasions, a ton of car parts, and last week I pulled a car up from Athens Texas with it.
So If you do a good (or even ok/adequate) job welding, the little welders will do the job. I have also welded together a drill pipe fence and other things as well.
If you all are having problems with sheet metal, get a copper welding spoon, or make one and back it against the sheet metal. It will pull the heat away and you won't get burn throughs. You can even seal small holes with it by doing a spiral weld backing on the copper because the weld wire won't stick to copper. Believe me, with the 47 jeep in my link, I learned how to do that quite well.
