Thats a good idea, I think that there might be a bit too much curve though.
I am thinking of maybe even building out coroplast from the bottom of it to get myself as close as possible, and maybe use some foam to seal it off. I have the pins bolted on at the back now, and so as soon as I mount the hinges to the roof it should keep a fair bit of pressure holding it down, so foam should seal I think (hope)
Edit: I just had another idea. I have seen pick up trucks with soft bed covers that have a handful of snaps on them to keep them down. I wonder if I could find and incorporate a few of those at the edges..
Or maybe velcro, but Im not sure if that would be strong enough, and how it would do with canadian winters.