Easy, cheap and quick terrain features can be made with stuff called Sculptamold. It is a premixed paper-mache, just add water and form it however you like. Earthworks are easily done by mushing together random globs of the stuff. Easy to clean up with water afterward. Usually dries overnight, depending on how thick the part is. Paint with your choice. I use cheap craft acrylics. Green colored sand is glued on with dilute white glue.
Here is how it looks. The bunker is 1/4 inch foamcore board, painted with acrylic gray that has some sand mixed into it. It got a wash of dilute black. The Sculptamold "earth" was just pressed up against the bunker--it has enough adhesive to stick. Brown acrylic paint and some green sand were added after it dried. The crater is formed simply by pinching bits of the Sculptamold into a crude crater shape. Painted with brown acrylic and bit of darker brown wash. The barbed wire entanglement is a random Sculptamold shape with broken toothpicks pressed into it. When dry, added brown acrylic and some green sand. The "barbed wire" is just copper wire wound around a dowel and given a little silver paint. The fibrous paper makes the pieces stand up under reasonable handling.
You can get the Sculptamold at craft stores (JoAnn's, Michael's, AC Moore, Hobby Lobby, etc). It is made by a company called AMACO. Our nearby HobbyTown USA has it. I think some WalMarts carry it and you can order it from Amazon.
I've already replied to this in an early, different thread; but I again applaud the application of inexpensive materials and even will try some of this once I locate the materials. Dang, I might even be able to model terrain a bit due to this info. TY box... for all the great ideas. You and others are such an inspiration to this non-crafty person.