The ideal humidity level should be around 70%. During testing I was getting around 22%. When I added the mealworms and a piece of carrot it was at 30%.
The humidifiers that are widely available seem too big for my set up and would be unmanageable for such a small volume. Foggers used in vivariums would also produce too much humidity and require an open tank.
Water gel crystals, used for keeping plants moist and humidors humid, might be a solution. I’m thinking of putting some in a small tub with a few holes in to give a slow release of moisture. I’ll order some.