If the humidity is riding low, and the snake goes into shed, I put some damp paper towels into the tub. A tub of damp moss that isn't even a hide can also work to raise humidity for snakes that aren't in shed--the moss has a lot of surface area, so releases the moisture better than a water bowl, and raises the humidity in the entire enclosure.
Having it in an open tub decreases the risk that your bp will spend all their time in there, and wind up with skin issues.