Well, my problem here is that I'm not totally sure the terrarium itself is waterproof. This a four foot by two foot terrarium with plastic bottom. It contains probes, wires, and a heat pad of some sort, which likely shouldn't be completely submersed
Well, then it's a no brainer. Tupperware containers. I'll expound later. Or, build a'mini tank' out of plexi for a portion of the tank.