If you are using a screen top try covering most of it with a towel. Just dampen the towel with a spray bottle when you need to bring up the humidity. Just remember to change the towel often, and watch out for mold. It's easy to get, and not good for the snake's.

You can also add some damp moss around the tank to up that humidity. If you need to heat lamp keep it, if not get rid of it. They dont need a lamp unless you are having trouble keeping your ambient temps between 75 and 80.