Steve, I have thought about doing this on my Honda, and what I figured the easiest thing to do was build the kamm so it is "Pre-Stressed", with the front of trunk/bottom of rear glass area being held up, while the top of glass & back of trunk are touching. Then put in some sort of hook brackets that grab the front edge of the trunk lid, put 2 straps to the center area of the kamm off to each side a bit, and when you tension the strap, it puts force on the front and back, and cinches down tight. Depending on what you build yours with, the gap could be ¼” to 1”. I never got mine started but I was thinking ⅜” would do. I was going to be very rigid.
It wouldn't move because it is locked in by the angles. I wanted to do this so my contact points wouldn't be on the paint. It would be the top of rear glass and tail lights. The only thing I have not figured out is how to do the strap for sure. I was going to make mine with a wood frame and cover it with styrene insulation board. That way it would be rigid and I could shape the foam easily into a nice radius. I planned on putting a piece of lexan in the rear upright area to see out of. I was going to make that about 9" on my car. It would have been a little above the template, but that is preferable for optimization to being below it.
A little sketch of what I mean.
My idea for the Honda.
