There are a few things you can try. You can try wrapping half of the screen with plastic wrap or put a damp towel on half of it as well. You will have to continuously make sure the towel is damp though. I did this when I used tanks and it worked out pretty well. You can also make a humid hide with some damp moss in it. Please be sure to leave at least half of the mesh top uncovered for good air flow and I assume you are using a heat lamp also.