40 gallon zilla breeder cage or regular 40 gallon? What’s the dimensions? I use the pink foam insulation board you get at Home Depot. Taped to back and both sides of tank. Then have pieces cut to cover the extra open space on the screen top. I use 2 100w CHEs. No heat mat. 10” domes. Regulated by a herpstat, could do it with a dimmer as well. Before then I was using a 75w red bulb and a 50w red bulb, controlled by the herpstat and had no problems. Ambient temps in my house are 65, now lower than 63, sometimes 67. I believe my breeder cagee I’m using is 16” tall. Don’t have a problem getting 93 hot side/81 cool side. Didn’t with the bulb combo either, and both needed to be regulated via dimmer or thermostat to keep from over heating. The styrofoam helps a lot.