I use an oil-filled radiator to heat my snake room, but I have close to 50 snakes in one room. My ambient temp is usually around 77-78. My hot sides in my rack systems are kept at 92. I do not worry about my cool sides. The snakes will move around the cage to thermo-regulate. If the cool side is too cool, then they will not go to that side.

Tanks are much harder to heat and hold humidity than tubs. Also the snakes feel insecure in tanks. Tubs are in my opinion a much better choice.

Hope this helps.