is 36x18 ok?

[Malum Argenteum]

See he was in a VE-70 equivalent before I went with a taller 120qt in an effort to be more naturalistic and it seemed he was more active in the short tub lol. But that could just be recall bias. Thank you for your input.

Possibly the "more active" behavior was because he wanted more room and once he got it he felt at ease. Or it could be that he liked the smaller tub better for reasons that we keepers have trouble seeing. I occasionally (not frequently, but a handful of times) have upsized growing snakes only to have them completely stop feeding; returning them to the original (too small, as far as I can see) tub immediately fixed the issue.

I have two rainbow boas like this right now, still jammed in shoeboxes since they won't eat at all in the next tub size up, but never refuse a meal in the shoeboxes. I personally try to give animals what I think is right (based on other keepers' input, natural wild conditions, empirical research, and so on) but if the animal indicates that this isn't what they want I try to defer to the animal's apparent wishes so long as it doesn't involve something obviously opposed to its health and safety.

Back to an earlier topic: having the tub in a rack, or using a PVC display enclosure, simplifies heating tremendously. The AP cage especially -- one radiant heat panel on a Herpstat and you're good to go. The Xmas tub in a rack in a cool room might need some creative heat tape (some belly heat, some side heat) but that's not too challenging. I share the worry about a CHE hanging over a tub, though of course you're the only one with eyes on the setup.

Given the lifespan of BPs, amortizing the cost of the most secure, safe and (in my opinion, anyway) easy to deal with enclosure comes out to a couple dollars a year ($250 APcage + $100 RHP + $200 Herpstat = $550 over 40 years = $13.75 per year), even ignoring the high resale value of this sort of equipment. Just a way to think about it that it seems we sometimes don't, that's all -- not implying that you or anyone else should see things only one way.