To make the tub seem smaller, you just need to break up the visual lines. Take a few sheets of newspaper, loosely crumple them, and fill the tub. It doesn't impair movement of the snake, it is easy to clean/replace and it makes the snake feel like it is in a much smaller and more secure cage.
In the CB70 tub, I would use maybe 5 or 6 sheets to fill that visual space.
This works great for new arrivals, shy animals, and lizard species as well.