That's where you might run in to problems.

This is what I suggest:

Get a large heat pad, which covers approximately 2/3 of the tank. Set the temperature on your thermostat at about 80*.

Then get a smaller pad, covering approximately 1/3 of the tank, and set the temperature here at about 90*. This way you'll have an excellent thermal gradient.

The same thing can be accomplished in a tub.

You'll need two thermostats though...
But the thing is that im only 16 years old and this will be costing me alot of money, and also the only reason i am aloud to get another bp is that i was planning on building a cage from a dresser and keeping both snakes in the cage but now i told my parents that i should have two different cages and now their saying that, thats not a good idea so thats why i wanted to keep both snakes in one cage. See my problem, im luck for having one snake