just get a 6quart latch box the king with the locking top. the tub may not fit in your rack height wise, so the latch/locking top should take care of that. (don't forget to poke air holes.) it would be just enough space for a hide and waterbowl. my hatchlings have thrived in this set-up.

if u are looking to go bigger, get something like a 15quart. That would be enough room for 2 hides, waterbowl, and a fake plant of something for a little clutter.