Foam pad on window in RV door: monofilament holds it in

Back when we owned a popup and later a hybrid I used Reflectix in each of the tent windows, trapped between the screening and tenting. The difference in hot weather keeping the trailer much cooler and in very cold weather keeping it much warmer was dramatic. I'd expect you'd find it much more effective for this application as well ... sold at big box home improvement stores like Home Depot, Lowes, etc.