So I've been searching for a product that is aquarium safe and would allow me to make my own aquarium decor and backgrounds. I came across this product though a bit pricey I think this is great especially if you want to design your own paludarium or background.
https://www.smooth-on.com/products/free-form-habitat-black/
https://www.smooth-on.com/products/free-form-habitat-black/