Just bought a 32 qt 5 drawer snake rack since I'm getting more BPs. Any how I was wondering how many holes I should put in these tubs for proper ventilation and humidity. (can't put my snakes in the rack till I get these holes drilled )

Also If you have any advice how to make the holes nice and flush with the others and without cracking the tubs I'd appreciate it, I'm weird when it comes to doing stuff I have to get it perfect.