I made the background. It is composed of a layer of silicone, great stuff foam, another layer of silicone, and a mix of organic soil, coco fiber, and gravel.
Its really easy... check out my 70gal thread or google coconut fiber backgrounds.Mind giving a how to? or pointing me in the direction of your inspiration. I have a 20 gallon sitting outside gathering dust and would love to make it a paludarium, plus the wife is on board enthusiastically