But the humidity inside will be absorbed and released into the wood and out of the wood again (dryrot)Kieth Moon put water and goldfish in his drink holder floor tom !! They are tight.
Moonie had an acrylic kit built to hold the fish. It was a custom clear plastic job. The video is up on YouTube for the curious. Horrible playing, but an interesting visual.
Typical wood kits do not seal airtight. Humidity is a measurement of how much water the atmosphere can hold at a given temperature and pressure. That has nothing to do with the air molecules moving about. If one believes that a single oxygen atom bonded with two very small and simple hydrogen atoms are too large to pass in and out of a headed drum, then I would suggest that individual has not fully grasped scale.
We are losing sight of the points here.
Let's not get caught up in this minutia.