I don't use a kennel, my dog is an indoor pooch but you can get kingspan insulation, about an inch thick, but it's quite expensive, polystyrene sheeting is much cheaper, about £10 for an 8X4 sheet one inch thick, cut it to size and put an old piece of carpet over it so Fido doesn't scrape it up with his feets, then put his bed in there and he'll be snug