New BP tank advice

[Bogertophis]

How tall is the tank he's in? Another way of giving more space to explore is by arranging things to simulate "2 stories"- something to think about- to make better use of the space you have, without all the air space in a larger tank that's hard to control (for temps). BPs aren't big climbers but they do enjoy "furniture" that's not too tall, including tunnels/hides.

You might think about finding or making something that that covers (like a massive hide) 2/3 of the floor- something that's about 4-5" tall (to allow for snake + substrate height), & the 1/3 not covered by this can be for the water & cool hide. The 'giant' hide would be over UTH, helping to contain the warmth & be like a cave for him, & the flat top could be for other furnishings, with the warming light overhead about midway (adjust for temps. on cool side). The overhead warmth will actually reach the top "shelf" better anyway.

I've done something similar in the past for a large boa- I built it & she LOVED it- I put a non-slip carpet mat on top (washable!) for traction, as otherwise the top will be slippery (snakes love substrate that gives traction). She spent time in the "cave", but also a lot of time on top, basking comfortably. You wouldn't have to completely enclose that 2/3 warm side, but do something more like a shelf that has cozy hides underneath, & openings on either side for access. (I hope this makes sense?) Anyway, I worry less about appearances for me, & more about what my snakes really enjoy- which can take some creativity. But this is your show...

Your snake is still pretty small for a tank larger than 40 gal. right now, IMO. I'm glad you've had him for a while & thru one winter now- but just think, if heat was a challenge with this 40 gal. tank how much harder a huge tank will be to keep warm. Just saying. UTH can only do so much. The most important thing is the snake's health, which depends on heat & humidity (& food). Hiding places are for their sense of security (avoiding stress) which also keeps them healthy. You're on the right track- we all made mistakes when we were new keepers.

What you describe as his cool hide (open ended bark tunnel?) doesn't feel secure to him, that's why he doesn't use it much. I recommend these & they're easy to clean, not expensive, from Reptile Basics: (be sure to measure your snake's coiled body, they come in many sizes)
https://www.reptilebasics.com/medium-hide-box

Bottom line- there's more than one way to do things for snakes- as long as you cover their needs.