The old "it's not a problem, till it's a problem" thing.
We are telling you this because we are trying to help. Please take what we say into consideration. We are saying it because want you to have the most time with you pets and not lose one to an accident. Many of us have been keeping snakes for years and years, we have seen the issues cohabbing can cause.
Yes in the wild the share the same range, territory and habitat, but don't spend prolonged periods of time together. The only exception is hibernation, and that is purely OUT OF NECESSITY. They also have many many square feet of woodland to explore and move away from another snake or species of snake they encounter.
20 gallon viv is not equal to a territory in the wild.
Get some shoe box sized storage boxes and make the bull snakes their own tubs. They are super cheap. Stack them on top of each other and get one UTH. Cover the sticky side of the UTH with foil tape and use it as back heat for the two tubs. Please make sure it is regulated in some way with a lamp dimmer or thermostat.
Total cost:
2 Shoe Box Tubs: $2.99 each (cheaper at local Walmart or Kmart)
Link for online purchase.
1 UTH: $17.59 for small Zoo med heater (could be cheaper at local pet store)
Link for online purchase.
1 Roll of Foil Tape: $5.99 (cheaper at local stores)
Link for online purchase.
Lamp Dimmer: $10.03 (could vary, but always between 10-12)
Link for online purchase.
Total: $39.59 but you could probably do it for around $30 by shopping local.
Or visuals....
How about some photos? Many from this very forum.
All images copyright by original owner.