In the long distant past, when I wore a younger man`s clothes, I was a wargamer and heavily into 15mm Napoleonics. Even before I had a go at making my own 25mm figures from sculpting to casting, I would make my own scenics using rolled up balls of newspaper, cover it with strips of paper, give it a coat of papier mache, and paint it with whatever was to hand once the whole thing was completely dry.
What a laborious and time consuming method for making something which, frankly, had no real durability.
Polystyrene was around then, but I had never considered using the lovely stuff. It`s light, can be sculpted with just a hot knife, and when given my "special finish", has miles more durability than the stuff I used to make.