Hey Rusty I am a bit more than less person The new version has 1/4 holes 1/4 inch apart, two rows, top and toward the bottom (4 rows in total with skipped bits where the hinges are). You could likely go less there is no exact formula. I tend to go more as there are documented ri issues with too little ventilation.

http://ball-pythons.net/forums/showt...ons-The-Basics

The new one has holes on the opening part only, the main 'plug' is hole less as Lucy kept pushing substrate out the lower ones.

The position high and low helps to keep air flowing by the convection currents. You could start with less and add if you need, I have a number and humidity holds well, but drops in a few days when it is really dry.