These hand sketches are intended to show the general construction are only an approximation in the size and dimensions of actual materials used.

The two images below show cross section views at the receiver mount centerline and at the frame flange area. I thought it would be better to develop the needed strength using a space frame approach (bracing along the lines of force to multiple attachment points with lighter gauge construction) as opposed to using massive thickness in the materials (for twisting resistance, for example) attached to a few points on the frame.