I use a very large cardboard box in an unheated room in the house (the sort that fridges get delivered in) and leave the infra red at the same height for three weeks, so they can move near it if necessary, then turn it off during the day a couple of times, then all day and then they're outside in a purpose built run (solid sides, flat top that's half clear Perspex and half wire) in a barn for a further three weeks.