Missiles cowl repair needs help

Andrew, I think you answered your own question when you said "after each small section of welding". On any thin sheetmetal, such as you find on all vehicles, you have to basically stitch weld with the mig, and then jump around from one section of the weld to another section so the heat doesn't build up. If you attempt to run any length of bead, no matter how small, you WILL get warpage. One short buzz, move to the far opposite side of the patch, buzz, then half way in between the previous two, buzz..... and so on. Keep moving around the work, and keep putting in very small "buzz" spots, and keep doing this until all the edges are filled with weld - run NO beads. :)