I have a 150 watt CHE that is one a dimmer with my glass tank that gets the appropriate temps. To help insulate the tank I picked up the stuff below and adhered it to the bottom and back of the tank using foil tape. If need be, I also have a piece that is cut to place on the top of the screen lid when necessarily to keep the heat/humidity in. My CHE is also on the same side as the UTH, this gives me a nice gradient temperature on the cool side.

http://www.homedepot.com/p/Reflectix...f#.UsR1VfRDvNk