We have just added extra layers to our girls hutch, we've stuffed some old pillows around the edge between the hutch and shed, they have a greenhouse heater, which is permanently on, in the hutch and a snuggle safe each inside fleece houses and lots of hay, they are currently in the shed so sheltered from the elements, the thermometer is showing 12 degrees currently, I'd like it warmer but they seem ok and have always lived outside so hopefully acclimatised.