My Cal King is 3 years old and about 33". I'm designing a rack system to house him, a couple corns, and some rosy boas. How much larger is he likely to grow, and what is a decent size Rubbermaid box for him? I'd like to give him something bigger than "adequate" since my collection isn't too big, but I'm not sure I can build a rack using underbed boxes. I know 28 qt. is the standard, but is there something a little bigger that would work well? How many sq. inches of floor space should I be planning on?