I kept my pigs outside when I had them (central Virginia in the late 80's). I just winterized the cage by putting plastic around the outside on 3 sides and thick bedding on the floor (it was wire) and also had a wooden box stuffed full of hay they could go in for aditional insulation as well as midnight snacking. I never had any problems other than having to keep changing the water because of it freezing. The pigs all seemed happy and never seemed stressed.