We have a 13' Scamp
. It does have a double layer of bubble insulation which does help. But windows
are the primary place for heat loss. We use ours during the winter as an extra bedroom when the kids/grandkids come for Christmas. I've slept in it when it was -10 F, but with down comforter and lots of covers - used very little heat except for when it was time to get up! Of course, it was winterized, so no water in system. With a heater I probably kept it around 30 degrees F. We love the shoulder seasons in Wisconsin - March/April, or October. Scamp
is made in northern Minnesota, so they do think about cold weather.