I am trying to weld three 1x3 11ga. square tubes notched across a 2x2 11ga. square tube. This would resemble a fish skeleton, where 1x3 notches are cut across the 2x2 tubing then the 1x3 tubes are inserted into the notches and welded. They are 15.5" apart on center with the first one at the very end of the 2x2 tube. It's warping very badly. The shop claims clamping won't help. ANY SUGGESTIONS ANYONE?