A lot of people cover their RV windows with Reflectix. Additionally, while Reflectix may help insulate, it also repels an effective free source of heat: sunlight! Some RVers put Reflectix in their windows at night and take it out during the day
If you’ve never used it before, basically you put double-sided tape all the way around the window frame, then cover the window with plastic stuck to the tape, and then you blow a hair dryer on it and the plastic shrinks and all of the wrinkles smooth out and the seal around the edges traps a layer of air between the plastic and the glass.
I did use one more window covering method last year, just for a few of my screen windows, and that was to make clear vinyl covers attached with Velcro. I did this so that I could remove the covers and open the windows on nice days.
Combining Window Insulation Techniques
1. Shrink film on the hall window 2. Bubble wrap on the window behind my husband’s desk 3. Plexiglass on my big windows. 4. Vinyl covers attached with Velcro on my screens and smaller windows.