Miniature orchids Terrarium

[Amyzes]

I am working on an 18 X 18 X 24 terrarium where I am going to grow small trees to mount micro miniature orchids on. I want it to look like a very small scene from nature, so I am putting a lot of thought into the backdrop as well.
I have built it out so that the bottom looks eroded like a cliff by water would look. I've used stainless steel mesh, slate, and fish safe pond expanding foam. The idea is that once it is covered in moss it will look like a small cliff face.
I am going to have an auto misting system and timer, so I am wondering if I need hygrolon beneath the moss, or do you think the moss can fill in the gaps of the mesh?
I've collected a bunch of moss, that i stuck in the freezer to kill any bugs, next is to boil then bake it, blend it and paint it onto the backdrop.
Is there another cloth I might use instead of hygrolon? Mostly I want to give a base for the moss that won't rot.

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