I originally planned to use automotive type window tint film, but found it expensive and boring, with various uninteresting shades of black, grey and brown it would indeed keep heat and light out. And make the trailer seem like a portable dungeon.
So I looked at Home Depot and found this:
Artscape 24 in. x 36 in. Magnolia Decorative Window Film-01-0113 - The Home Depot
Cost $21 and will cover more than one RV door window (at least 2, maybe 3) and comes in several interesting patterns.
Install is a typical wet the film and glass with soapy water type install.
However, the inside part of the door glass has a textured finish to it and the film will not work well if at all on the textured glass.
The outside is smooth. Therefore the glass must be turned around.
You'll need some sealant to seal up the window again and a razor blade to scrape all the old seal off the glass and frame. I recommend against the use of an electric screwdriver as the plastic frame seemed easy to strip out. Also recommend a helper since the 2 frame halves AND THE GLASS will fall right out once the last screw is removed.
Extra hands will help especially during reassembly. Apply the window film per manufactures instructions while you have the glass out of the frame for the best looking results.
No, it ain't
real, but it ain't real expensive