I have a 20 gallon long with a 100 watt CHE and the warm side is easy to maintain at 90 degrees but the cool side drops to 72-73 degrees no matter what I do. I have acrylic over 2/3 of the top but no insulation.

I thought about insulating the tank but I’m tired of dealing with heat and humidity issues all together. I ordered a PVC enclosure and a radiant heat panel.

Insulation would get you where you need to be if you want to keep the tank.