From what I read about product; this thing is nothing more than a plastic container with a sponge inside. You add water to moisten the sponge and connect an air pump to pump air through. Obviously exiting air will become a bit more humid than incoming air; but I would not expect this thing to do any miracles. If the enclosure is small, maybe it will help to raise humidity a bit. They are telling you to cover the whole top because the item is relatively inefficient and you will not see any if little gains if you don't do so. Good luck !