A tig welder also does not spread the heat nearly as bad. It is a little tricker to weld with, well more getting used to it and learning it. But tig welders are expensive, and not everyone has one just laying around. I cut my fenders out and ended up warping the sheet metal a little. the copper is a good backer for your gaps, the weld will not stick. As everyone else has said practice, patience and space the welds. The reason my fenders warped was because I didn't let my small stiches cool enough before going back and adding the next stich. The side that ended up looking the best was because we couldn't get the welder to work right and could only get small tacks rather than a continuous bead. Keeping the heat down is the key. thiner wire and mixed gas really helps.
