-"When I get some final dimensions, I'll engage with some local canvas/tent making vendors to discuss material options and design. I don't expect to deviate far from the 'windows/screens on all sides' design that the other guys have."
In the past, the bicycle trailer company "Burly" in Oregon has been involved with a few special projects that don't relate to the bicycle industry. At one point, they were making all of the canvas and associated waterproof components for Tentrax trailers. Burly makes great products with top notch craftsmanship. It was probably the nicest part of that Tentrax...
I can't wait to see what you come up with for a top.