I think you should be good to go. I have less open air space than that on my tubs. I have about 6 holes on each end of the tub to control my humidity. I stay at 60% with the waterbowl on the cool side. When they go into shed I put the waterbowl on the hot side and it gets 80+%ish. I haven't had a bad shed yet.

Regards,

B