is 36x18 ok?

[Malum Argenteum]

I would like to add that some manufacturers like Boamaster and AP make racks for those big Christmas tree tubs if you wanted to get one.

That's a good thing to mention. I did have mine in a rack, for what it is worth. They were too large to slide out easily (heavier snakes than BPs, admittedly) and harder to clean than stacked enclosures (either put them on the floor and scrub them out, or try to move them somewhere to hose them out -- neither was as good as working in a front-opening AP cage).