Don't tape the holes up. What if they flick their tounge in the hole and it gets stuck! lol well maybe I am being a bit over the top but you can just as easily hot glue them closed.
I would say just leave one row of holes in the front and one row of holes in the back and see what that does for your humidity.
I agree. If you don't have a hot glue gun, you can tape a small piece of paper or plastic wrap, or wax paper over the hole, just so they can't have access to the actual tape...