I had one of those exo terra 18s for my BP. What I did to raise the humidity was very simple. First I bought a sheet of 1/8 in. plastic to cover the top screen, and cut a 3. in dia. hole in the top for my heat lamp. then I fed an air hose through the back with a 10 gal whisper quiet pump on one end and a small air stone on the other. I put the stone in a bowl of water. It bubbled and splashed all the time. All I had to do was put water in the bowl occasionally. It was a great expedient, until I bought a tub setup.