I use the silver bubble reflecting material. Cut just a little larger than the window and force fit in the frame that way you can pull it out when you want light in the area. It also helps keep you cooler on hot days..
2004 Chev Silverado Duramax optioned past the max. 2009 Jayco Eagle 308 RLS 765 watts of solar, 6-6 volt batteries (696 amp hour), 2000 watt (4000 surge) whole house inverter.
215 days boondocking in 2016
211/2015, 196/14, 247/13, 193/12