Thanks for all of the feedback. Believe it or not, I had a dream about that design.
To address a few you your guy's concerns:
First let me say that in no way was that drawn to scale. I did it in 5 min. in MS paint. I need to do some refining.
2) That actually is the proper way to attach a piano hinge. Take a look at piano some time. That is structuraly stronger than laying it flat.
3) I plan on using a hardwood rib on both the roof & hatch where the hinge attaches. The white is FRP panel.
4) Ther caulk was more to devert water when it is closed. I may put caulk between the rubber & the spar/roof & no bead to top.
5) I know of some rubber products used in roofing I was going to play with. They resist UV damage.
I do not see me using my trailer more than 5-6 times a year. Mostly in the spring & fall. When it is not in use it will be tarped. I figure the rubber may need to replace ever couple of years. (if I don't build a bigger one.)
Keep the comments coming, my may just talk me into a Hurracane Hinge....