Well I use a tupperware container with a hole cut in the top, as do most people, but if you want a realistic looking one you can take a rock formation or something at a pet store, basically anything that has a bottom and can handle moisture or you will get your substrate all wet, then just run some of your moss under warm water and ring it out so its just damp, place it all around in your moist hide, they'll do the rest. I like to put a damp paper towel under the moss as kind of a liner at the bottom.
