If you are having trouble with humidity, double milled cypress is the only thing that retains enough moisture to make a difference. That and tubs.

I personally don't like cypress mulch because its too dirty. I don't like cleaning dirt. It seems counter-productive to throw dirt into a clean cage only to clean it out in a month and replace it with more dirt.

I know you were thinking about switching to tubs and I think it might be in your best interests if you do. Having that many snakes in tanks can be a chore when it comes to cleaning and managing your husbandry. Tubs make your life tons easier I assure you.

Over all, I would say the best substrate is paper towels. I always keep coming back to it.