You don't have to move the snake from a tank, especially if they are relaxed and like the tank, just because of humidity. Just use the foil treatment or plexiglass over the screen top and make sure the glass is insulated and voila!

But if you're dead set on a tub, they can be on their own without a rack. Just make sure the lid also has ventilation holes and use mini bungee cords to hold the lid secure. I used those, and even adult BPs and young corns couldn't get out.

Just keep in mind that all snakes are different, and they all have housing preferences. I had several that just would NOT eat or settle in a tub that did perfectly in tanks.