My tubs have no holes at all. There is enough of a gap between the edge of the tub and the rack that there is enough ventilation. Plus every tub is pulled out twice a day for a quick check and to completely circulate the air in there.

Many people do not need holes in the tubs. Unless there is an air tight seal between the tub and rack which isnt possible. The biggest reason people put hole in tubs is to decrease humidity. This is usually needed in smaller tubs but not with big ones. Unless of course the tub is not in a "shelf" and is being sealed off by it's own lock down lid.

Snakes dont actually breath very often when at rest. They have very efficient body systems to preserve energy.

So you can do one of a few things. Switch the tub out and start with less holes. This may mean you need to set your thermostat a couple degrees lower to compensate. Or switch substrate to something that holds humidity. Or take one hide out and replace it with a larger water bowl. Many snakes in racks/tubs do not need hides if the tub is the correct size and they are not exposed to unnatural light like lamps or room fixtures.