Happy to report I finally began constructing the Steve-Sanford-Style situp blind similar (almost identical) to the one depicted in this thread. If Steve S reads this I'm hoping he can recall whether he put any type of horizontal piece at the bottom of the port and starboard luan sheets to provide rigidity. It's clear from the diagrams and photos that the top and sides of the luan have such structure.

Thanks for any input.

By the way, we also plan to take Steve S's suggestion of making the top flap shorter (just probably not as small as Steve suggested, but then who knows, if we get in to model it we may find the suggested length is right.