I could add a rail at the top but I think it'll be easier and more adjustable if I just pull the canvas tight and use screws. I do like your idea and I may try it depending on how well the sewing goes for the lower rail. I have a good sewing machine but lack a good working area for such a large job so I may keep it simple and sew as little as possible.
Thanks. I got the rivets from Mcmaster Carr.
Not sure on the seal yet. I'm thinking a small bulb seal around the outer edge or a larger bulb seal like this....
Option 1
View attachment 654805
Option 2
View attachment 654806
The tapered hard rubber bumpers are to help align the top as it comes down as well as a resting point while it's down. There's only an 1/8" gap so option 1 would seal that up but wouldn't allow for inconsistencies or movement while driving . Option 2 uses a larger bulb seal which would allow for more movement but might rub on the canvas which isn't ideal. I may be overthinking this haha.