I have four ball python tanks set up. all identical, all perfect. I have the UTH on the hot side, set to a constant 94 degrees with a simple 10 dollar lamp dimmer from home depot. it covers approx half of the tank. I have the CHE Off center towards the cold side. I have it hooked up to a $20 500R thermostat. the thermostat probe is on the floor of the tank, in the back corner of the cold side. It is set to 82 degrees. Water bowl in the middle... 2 identical hides. for a 20 gallon long you should be using a 60 watt CHE. For a 30 gallon long you should be using a 100watt CHE. put foam board on sides and back of the tank. Cover the top with foil, then duct tape, leaving only a hole for the CHE. Your origional pic looks like the acutal CHE lamp is too big. you may be able to use it... but the whole in the foil may be too big. ( you may need to get a smaller lamp)

You must have the CHE on a thermostat. a 60 watt CHE at full power is about 130 degrees an inch below the bulb.