I started out by stitching the cabintop together on the floor of the garage---that's the wrestling part. There is a substantial twist in the cabin sides that the plywood does not want to do. I also found that the pieces as cut in the kit do not want to completely come together toward the front of the cabin top. No big deal, the small gap can be filled with silica-thickened epoxy before taping.
The trick to getting the front edge of the cabintop flat is shown below. After stitching, I "squeezed" the cabintop down between two 2x4s until the front edge was essentially flat. I then laminated a 2" wide strip of plywoodto the underside of the front edge with a piece of 9oz tape in between. the tape was 4" wide so I wrapped the tape to the topside which served to resist downward bending in the forward edge.
After an overnight cure I released the 2x4 "clamp" and there was only the slightest curve in the forward edge of the cabintop.
From there I lifted the cabin top into position and stitched it into place starting from the front and working my way back from the center to the outboard edge.
Filetting and taping the under side was routine. The only thing we did prior to that was fill the gaps (1/2" max.) between the side and center panels (see above).