Ball pythons came from areas which are fairly arid. The burrows and mounds they use as dens are considerably more humid.
I bring this up because it is not critical that you maintain high humidity in the entire enclosure. What is important is that you provide an area, like a hide, where he can go for increased humidity.
It's alot easier to provide a humid hide than to constantly have to be spraying, misting or employing complicated methods in order to bump the humidity of the entire enclosure.