Thanks for the input - will continue using a piece of plywood or 2x6 on the roof/hatch 'kind of' works.If I had to guess I would say it wouldn't work. They may support the downward force if you box the setup tying it all together at the hood line, but I could see it racking if there is any shear load. It'll definitely rack if you extend the roller up to your roof line unless you triangluate it somehow as well as tie it into your roof rack.
Backwards mounting may or may not work. I haven't tried this. There is a relief cut in the mount to accommodate the curve in the hood line where the mount sits.