I kept a pair outside here last winter but locked them inside the retreat with a 100 watt light bulb during that incredibly cold 14 days or so last year. In the mornings because the box was made of plywood I temp gunned them in the middle 40's but in the day the body temps were in the hi 70's. They did not get sick and I finally sold them in July.....thanks
-----
Tom Crutchfield
www.tomcrutchfield.com