If you purchase a rack from Animal Plastics, Boaphile etc. They will come with a strip of flexwatt "snaked" through the rack. It's toward the back of the rack, creating the hot spot.

The tubs hold humidity very well. The rack also does better in a room with a steady temp.

The flexwatt controls the hot side temp. The room temp controls the ambient air temps.

An enclosed rack is nice and dark in the back of the tub.

I have lights in my snake room set on a timer. It's bright enough where it gives them a light cycle.