Don't bother, the thing doesn't hold humidity worth a bleep. Even with all the holes caulked, I couldn't get mine past 80% humidity. I guess it's fine if you are incubating in separate sealed boxes, but it's such a small incubator, that's a big waste.
Just get a Hovabator, remove the wafer thermostat, and hook a Herpstat up to it. You'll pay $20 more total, but you'll be able to put water directly in the base, set a light grid over it, and fit up to 5 clutches in there for substrateless incubation. That's what I am doing, and it is working beautifully.