What are your ambient temps in the room?
To reach my goal in my room which gets down to 68 at night I am currently using 2 UTH's(on thermostats) and 1 60watt CHE (on a lamp dimmer).
The UTH's get the warm(92) and cool(82) side to their perfect temp but wouldn't increase the ambient temps in the tank more than 2-3 degrees. So I am using a 60 watt CHE on a dimmer at half power in the center of the cage pointing straight at the largest water bowl -but I have to refill daily(this increases ambient temps in the cage and also doesn't kill my humidity completely). I am also using a 2nd smaller water bowl on the cool side to assist with humidity and also provide a water thermal gradient.
I covered 3/4 of the Lid with 3 layers of tin foil, then covered that with a black duck tape for aesthetic reasons. I have the back and sides covered with a black foam board(the project boards that we did presentations in high school/ college with)
I have held this tank like this at perfect temps for about 1.5 week now and I have tested my temps from 62-85 and it held steady with ambient temps in the cage ranging from 79-85. Although I don't have my snake yet and I have already made the purchase of an Animal Plastics cage.
I realized that this will be a pain to clean and maintain the temps/humidity correctly all year round.