Well there are several easy fixes to that:
Water sources:
How many water bowls do you have in the cage? You might try adding another dish of water, or using a larger shallow water bowl (like a cat litter box) I know you have the fountain, but sometimes just another pan of water will help
Substrate
What kind of substrate do you have?
Cypress is good at holding in moisture,
Coconut fiber (or forest bedding) is small enough to not cause serious health problems if its ingested, and holds humidity quite well..Mine always got it in their eyes though, and that's another con to the coconut fiber.
Peat moss has been used by many CWD keepers with success and holds humidity well
Misting Systems & Humidifiers
An automatic misting system is a good device as well, and not horribly expensive for a small one.
A pot of water on the stove simmering helps my humidity
I think BWSmith has a ghetto humidifier do-it-yourself topic he made that was cheap, and works well. I'll link it in a minute

A standard humidifier in the room near the cage would help.
Honestly 70% is good for them, and raising it to 80% by adding another bowl of water, misting more often, or adding a humidifier just when you notice the lizard shedding is usually sufficient.