Low tech solution
When we camp in freezing temps, we often get ice on the insides of the windows. This is despite the foam inserts that we use to cover and insulate the windows. We leave the bathroom hatch open a little -- but if we leave it wide open, the trailer gets down below freezing.
So here is the solution -- as soon as we get up in the morning, we wipe down the windows with a towel! Not very high-tech, but it works.