Don't try to run a continuous bead. Skip-weld in several areas, never more than 1/4" at a time, and move several inches away for the next stitch. That keeps from distorting the panel due to big temperature changes. It also helps if you have several patch panels test-fitted and tacked into place so you can switch to another place and make a few welds while things cool down at the first weld site. Then go back with an angle grinder and smooth up the weld beads after some cooling happens. Definitely run the smallest wire you can find, hot and high speed.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!