This is one of the thoughts behind me putting my reflectex on the outside of the window. To keep the window seals cooler..and to increase the effectiveness of the reflectex in keeping RV cool. I use heavy duty Velcro on mine with a few patches on each window. Maybe less attractive, but black is pretty subtle on the tinted glass..and I think the most effective. If someone else tries this, use the big patches of HD Velcro, cut to size, and prepare for occasional replacement of the Velcro and the Reflectex.
Prior to the Velcro I used suction cups to hold the Reflectex up. This was more maintenance intensive as the (HD) cups were always failing, and needed a constant stream of new ones from Amazon to keep it going. Velcro has been the better solution.