C channel frames are pretty much the same between brands and with that in mind the frame that gave the least trouble when we were pulling was was an unboxed Ford pickup frame with a 1500hp Arias engine. The next least troublesome was a round tubing frame on a 4 (or 5) engine pull tractor with a twist factor designed into the frame. By far the most cracking occurred on the short, rigid, triangulated and cross braced everywhere sprint car and super modified all round tubing frames. If you do box a section of a frame leave a 60 degree taper at both ends or even better a parabola shaped cut out on the ends of the boxing plates. This lets twist transition from flexible to rigid over a spread out distance rather than concentrated at one point which is a crack waiting to happen.

Evan