yeah a 24x18x12 = 22.4 gallons... seemed small to me too (especially after adding dish, hide, etc.). I was prepared to buy the large 36x18x18 but the local snake expert said the med/low was more than an adequate footprint/size for a BP, + 12" is a preferred height over the taller ET enclosure for BPs... was advised to cram it up w/décor if I bought a hatchling (= more security) and remove stuff as they grow to open up more space. I did have issues maintaining humidity which was resolved by covering the top screen sections with acrylic and switching to eco earth.

Good luck with your path forward (and 4 dogs!). I'm sticking with just a snake and med/low exo-terra.