For adults, there is a little more flexibility. I house adults individuals (as with all non-breeding snakes) in either 3x2foot or 4x2ft cages. I use Vision brand cages, but Neodesha and others also work as long as the following basics are met:
A proportionate size hide box for security, a large water basin with fresh water and supplemental heat to provide a proper thermal gradient. I find the heat source is very important in many ways. For one, I have not had good feeding response from the snakes when I used a lighted basking spot for heat. Instead, with 11" heat tape running the length of one side of the cage to provide the same thermal as with hatchlings or the preferred source is an overhead radient heat panel. I have used ceramic emitters, but they get real hot and tend to dry the cage out too much. Too offset this, I place a larger water basin under the heat emitters and make sure the emitter is shrouded from the snake to avoid contact thermal burns.
Back to the heat tape, be very careful with using heat tape. STP's will camp out on the heat tape for days if the air temps are too cool. If your heat tape is set too high, you will get nasty thermal burns. They don't sense the pain from this or at least don't associate the pain with the source of heat.
Please keep in mind: This works for me and is not the only solution to housing the snake. Variants to this are dependent on your ambient room temps, quality of caging, health of the animal, etc. So do your homework. I have been keeping STP's since around 1996 and continue to learn each day.
Good luck.
