I have the same reservations that you do about this design. I'm not sure I like the boat being the tilting frame itself. Not sure I like the raised hull just up there unsupported. I'm definitely going to build mine out of steel.

Regarding using the boat structure itself as the tilting frame, it was mentioned on the tornado group that because you have a rack itself does not isolate it from flexing. However, I think that a steel rack with diagonal tensioning rods would flex less than a free standing unsupported flying hull. They say the loads on it would be much less than a boat crashing through a wave, but I'm still a bit skeptic.