I'm with Warren...I'd not be comfortable at all with any weight aft on that structure. In order to gain adequate support that would withstand wind loads, I'd think you would be looking at something far more substantial - and expensive.
i've been looking at various ways people have been attaching kayaks to 22's for the last few years, but thought of something a couple weeks ago that is intriguing...and might work on your's as well. It's dirt cheap, with nothing permanent required.
You've likely seen the foam blocks used for car top carriers for canoes. My thought is to get a couple foam blanks, and sculpt them as necessary for my rooftop and whatever kayak I end up with. The finishing touch -
Rok Straps. I just discovered these for a motorcycle trip I'm about to take, and they would seem to be perfect for the marine environment. They hold like nobody's business...once side of the strap is rubber, so shifting loads don't result in them loosening. And, they have no metal parts to corrode, simple loop ends that would easily lash around handholds or rails, and they go off/on in seconds. They've a pretty stellar reputation in the motorcycle community, and they've performed well in off-road situations that are far more extreme than I'd expect to encounter on the water.
If you tried the above and it fails, you're not out much $$. However, if it works - you could then get a more traditional frame and canvas for the rear, that would be less expensive and more flexible - having the ability to go on/off in a few minutes, as opposed to a permanent structure. If the front of this canopy were designed such that it could easily be removed from the aft cabin, you could also fetch your kayak easily were it up there.
Let us know what you end up with...Ranger or C-Dory, many projects such as this cross over with minimal changes.
