body work approach

I'd go with .023 or.025 (thin) wire Mig with the shielding gas. The flux core is not well suited for panel work. Also, you'll want to make small/short beads, skipping around the area your working, Too much heat in one area and you'll warp your metal. Mig welds are not very flexable either, so make sure all is straight before you weld.

My 02, Eric