There are a few factors that go into my statement. The design of the trailer doesn’t lend itself to being well insulated. The main body of the trailer raises and the bed slides out the back. So there isn’t a continuous wall from floor to ceiling, there is a gap that is sealed by gasket material and leather. The walls are also pretty thin. Luckily the diesel heater is more than adequate. While Kimberley has done a number of things to help winterize the trailer, I personally just dont think it would be very comfortable down into the teens or lower at night. I wouldn’t call it a true 4 season trailer.
But you are trading that for something that is super compact when packed up and also reasonably light weight with amazing offroad ability. In travel mode its barely bigger than the offroad tear drop we had before this. But once opened up its amazingly spacious and comfortable inside.
So my personal opinion is that anything sub-stained below 20 degrees isn’t going to be comfortable for me. I also feel beyond that you are risking issues with freezing water lines.
Hopefully that helps.
Mark