I wouldn't let the insulation be a deciding factor for you. You can go to home depot and pick up a 4'x8' sheet of foam insulation board for right around $10 if I remember right. Cut it with a utility knife or table saw to fit the outside of the rack and attach it using velcro or double sided sticky tape. I did this for the rack I made when the snakes were being kept in my bedroom, which was kept at 70 degrees year round. The insulation kept the heat in the rack and with the flexwatt set to 94 degrees the ambient temperature in the tubs stayed right between 80-83. I'm pretty sure Connie has posted pictures of this rack in the past, but if I can probably dig some up if you need a visual reference.