I have used sphagnum moss and paper towels inside humid hides. (I currently don't use them) I preferred the paper towels because they didn't mold up quite as fast and when they did it was very visible. (and easy to change out)

I did not remove the other hides but usually just put the humid hide in the middle, but I imagine it wouldn't hurt to use it on either side. Although, it may be more prone to the mold on the warm side. I can't remember but I believe I changed the paper towels every third day or so.

I think it's best to maintain the proper humidity levels, and using the humid hides as a backup not a replacement for the proper husbandry requirements.