large welds on one side, means major warp, either minimize welds or use a strong back to pull or push out warp and or twist....sometimes a little force applied and some heat on the offending weld will take out the warp. At work, Bobcat company.....lots of time spent on robot welding sequence,part preload and other considerations.....still heavy mtl. heavy welds, definite problems to solve. On welding fixtures....many times the fixture frame was welded up then sent out to be "normalized" in a large oven....then finally machined. on one off projects like our trikes, become a study in straightening techniques! good luck...looking good!