I used motorcycle windscreen mounting screws and nuts. The nuts are rubber so it helps allow a little give at different angles when tightening down the cover. I used epoxy to mount them in drilled out holes. You can also use washers to shim them if needed.
Those are cool. I don't understand why you would need the epoxy? As far as I understand it from the ones I have previously used, the metal nut part does not run the entire length of the rubber. The idea is to drill a hole that is just large enough to fit the rubber thru without the screw in it. Then you put the screw in and when you tighten it the rubber expands and holds everything firmly in place, but still rubber mounted for some give. They are an elegant solution and I have used countersunk screws to make the window finish even smoother.