My airflow seams to be fine. I have been using the heat in Chicago since the weather isn't even for the birds. I used Lexan since it has greater flexibility than regular Acrylic. Thus, I do not think the heat will be an issue. If it is I will just fabricate a new piece using thicker material. The concept and idea remain. Make it serviceable.
I tried numerous adhesives (5 or 6). Anything from Epoxy, 3M plastic, Epoxy Clay, Silicone, etc. The issue was always the same. Think of it like a ice cube tray. If the tray does not flex the cubes remain locked in place. Twist the tray and the cubes fall out. That is exactly what happened with the adhesives. I test spotted the adhesives to check adhesion before spending time otherwise. This to me seemed to be the best solution. In addition, it was fairly easy to fabricate and install.
As far as the ducts go I cut the control arm and then removed it from BOTH ends. Thus, I would not have to worry about the cut pieces getting stuck on anything. The vents I removed. Then I drilled a series of holes through them and put them back in the closed position. Thus, I am letting airflow through them. It is just restricted by how many and what size hole you drill. It is a happy medium since you do not have to make a choice to only have it on or off.