From the OP's other thread: OP works for a veterinarian. The snake was brought in by the owner of a big box pet store because it has neuro issues. Pet store is relinquishing the snake to the vet/OP because it doesn't want to shell out a ton of money for testing & treatment; from a business perspective it makes more sense to write it off as a loss and get another one.
OP: don't worry about the tub size being too big, as a tub will be easier to maintain anyway, assuming it has a top that can be fastened securely, and clutter up the tub with loosely crumpled paper that the snake can hide under.
Get a heater and t-stat for the tub, or alternatively you could heat just the room that the snake will be in to 85*F.