Originally Posted by brownrecluse
Or do you have another idea for the windows
in winter camping?
: buy some 1" or so polyurethane or polyisocyanurate (spelling?) foam sheet and cut a piece to fit each window neatly. Maybe use cardboard to make templates to get the shape exactly right? Unlike blue or pink foam (polystyrene) these foams have higher R value but, more importantly, are very tough so they will withstand being handled repeatedly.
One piece of sticky Velcro at each end should hold them to the window. If you wanted to get real fancy, you could stick fabric to the inside for a nice appearance.
These would be a real nuisance to have lying around the trailer in the day, but that may or may not be much of a disadvantage as days get shorter.