When we lived in Alberta we left for down south in -35 celcius a couple times with our truck and fifth wheel. It is not ideal but we stayed in it 2 nights in cold weather on the way down with our 2 dogs. We left the slides in and made due and were quite fine. The worst thing we experienced was a frozen memory foam mattress. The following year we pre warmed our trailer for a couple days and that solved that problem. Having the slides in I think is easier to heat and less potential for things that may freeze up. Some RV's are not useable with the slides in though so that is another thing.