I just looked at several videos and it might be more helpful to use a paper, such as "
Rachel in Real Life" uses. I had not used backing, except with contact adhesive and back packing foam pads when we were ski camping at Mammoth Mountain in Calif. a number of years ago. The foam pads would help with hot areas also. There is very little R factor in even the double pane glass RV window. (We had all double pane in our Holiday Rambler 42' pusher which we owned prior the current Winnebago Via 25T.
I take careful measurements and then cut the Reflectix slightly larger than the inner window frame. I do use a sharpie, and some 3M blue tape to help hold in place when making the cutouts, I do the Reflectix first then cut the back packing pads to fit. For the windshield, you can buy a roll of Reflectix which is 48" wide--and that is wide enough, Also often you can sandwich the Reflectix between the shades on a Winnebago and the glass or plastic window. For the front window one might have to make the Reflectix very tight fit.
I have not used these for the Reflectix, but I do use rare earth magnets for the MagneShades which are external to the windows. I have all of the front windows on the VIA covered with the MagneShades, and could use those magnets for the Reflectix cover.
Bob Austin--celebrating 60 years of RVing
2013 Via 25T