I believe that it is not possible to have too much ventilation. I hole location and number and size all change air flow I personally prefer to have hi low hole high on one end and lower on the other to produce greater air flow. I also believe that if paper is placed in as a substrate and the water bowl is removed and the tub is basically dry it should equalize with the room in a short space of time. (1 hour or less ideally) Adding a snake to dry like I have described should never raise the humidity inside the tub if it does the snake is exhaling water vapour and it is not venting to the outside. The enclosure should smell fresh and a little like what ever substrate you choose to use and nothing else.

water vapour in the enclosure should be coming from water held in the substrate and the bowls not from the snake.