Increasing the air flow will drop the humidity. This can be done as simply as adding an oscillating fan to the corner of the room and leaving a ceiling fan on if you have one. It can all be done by adding more holes but I don't like to do that first as its permanent. While you can cover some unneeded holes with tape(only on the outside) it is not visually appealing.

Do not place a fan blowing directly on it. You just want to stir the air in the entire room without hitting the tub directly. I have to use this trick in my snake room or my pvc cages fog up and get way too humid.