Honestly, I have had complete sheds with 51% humidity.
A few options if you are using a tank with a screen lid:
-Lay a damp towel over the top to keep in moisture
-line the lid with tin foil or Saran Wrap
-get a piece of plexiglass cut to fit under the lid (obviously do not have the piece cover the entire lid)
If everything we have suggested doesn't help, you could also add a humidifier in the room where the snake is as well.
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