Well, technically, if it doesn't have a gas bottle, it's not a MIG, it's a wire feed welder. I use a wire feed welder for all kinds of stuff, and it does a great job. The only real difference between a wire feed, and a MIG is how clean the welds come out. And you make any weld look pretty afterwards by spending time cleaning it up. And the major difference between a cheaper welder, and one of those really expensive ones is the duty cycle. Most amateur welders like myself don't weld fast enough to worry about the duty cycle anyway. So you'll definately get no flaming from me. I've done all kinds of stuff with my wire feed welder, and you can definately do floor boards with one.
I agree with Husky, I would just give everything a good inspection, and if the torque boxes look good, you can clean up the metal, and weld an extra layer of sheet metal on top. Also, it would be good insurance to put some battle boxes in the car to make sure nothing comes apart. As far as I know, Wild Rides is the only company that sells them.
wildrides.com: The Leading Rides Site on the Net.
Kurt