Any welders on the board?
turn your wire speed down a few, and try it...and turn the voltage up or down from there.i run my gas at around 30" make sure its very clean (after grinding i wipe the panel with denatured alcohol)and that your ground is good. when welding your quaters, weld the upper seam (front to rear upper) in 1 inch sections about 4 inches apart and then go back and weld an inch more ,etc,etc until it is completly welded (this will cause very minimal heat warpage.you will get some warpage but very minimal)thiswill make it so you will not get the cracks and bubbles you get from just plug welding the panel (ive not fully welded the quater on one car i did and from chasis flex it cracked at the rear )