When I use cocofiber for my frogs (they need about 80% humidity) I expand it- or soak it, if it's the bags- so that it naturally forms clumps, and holds together when you squeeze it lightly in your hand. It usually holds its moisture pretty well, and that's in a tank and not a rubbermaid... Could you mix wet sphagnum moss in with the substrate? I used to do that for my box turtle, but she has such a horrible habit of eating bedding that I've had to remove anything that could be an impaction risk.