I have about fifty holes in my tub and the humidity is still hovering around 80% even with the water dish on the cool side. (There's no snake in there so don't worry about that.) So you could need a lot more holes or just what you have. You won't know until you have hides and substrate and water in there so just assemble it and wait to get a good idea of the humidity. Poke more holes or cover them up as needed, but I'm going to take a guess and say you're going to need more holes.