How good are Corns at escaping?

[joepythons]

I have a 32 qt tub rack system. The tub has an ever so slight gap between the top and the rack itself. I used a soldering iron to put two rows of air holes in the sides.
My 1-1.5 year old Corn has been hanging out near the front in order to, I suspect, look for a way out.
Is it OK to keep corns in tubs with no lid? Also, if I put the lid on, how many air holes are enough for the tub portion??

If he can get his head thru the gap he is gone .If you forget to close the tub completly he will find that gap for sure.They are great escape artists