I use a rack system with heat tape so I don't have any suggestions for a uth. I do know that the humidity will be very easy to manage in those tubs with a substrate that holds it well like coco fiber or Cypress mulch. Just make sure to drill plenty of ventilation holes in the tub so it and the snake can breath.
Thank you. My plan was to poke holes around the top perimeter of the tub and the lid.