Henry,
I racked my brain on this same topic and came to the conclusion that flapper boards work better on smaller cockpit, layout style boats. A large cockpit like yours is a bitch to hide and The Duck Boat Company blind is the best solution that I've seen. In fact I originally considered purchasing their boat but wanted a more conventional design for fishing.
You seem a little spooked about a sewing project but if you can stitch and glue a boat, sewing will come easy. Bending tubing is as simple as filling a tube with sand and clamping it to a form. Good luck with your design.
RM
