what are you using to make you holes with?
If you have a ceiling fan turn it on or a small oscillating fan to circulate air around and across the tub will help bring down the humidity.
I make my holes with a soldering iron from wal-mart. It cost about $9.00.
https://ball-pythons.net/gallery/fil...8/hpim0303.jpg
I have found that 1 or 2 rows on the long sides works good. If humidity goes too low. Cover one row of holes and reduce air circulation. If it goes too high then increase air circulation and/or open up some of the holes...