New tub, how many air holes?

We just got a 90 Qt. Sterilite tub for our 20" male BP. It is 35" L x 16" W x 12" H. How many air holes should I drill, where should I drill them and how far apart should they be? Thanks.

not quite sure on exact number, but remember you can always add more, cant take away ;)

I melted some holes in all 4 sides and the humidity was still too high once I turned on the UTH and placed the water bowl in the tub. It was reading off the scale on my digital thermometer/hygrometer (>90%). So I melted some holes in the lid and it is now better but still a little high at 68%. I think I'll leave it though as I am moving from Vancouver to Calgary in a month and the air is much drier in Calgary. Incidentally, that's why I got the tub and am ditching the glass tank, to make the move a heck of a lot easier.