It is not uncommon to build maquettes or proxies in cloth or fiberglass or whatever, and then send them out for final surfacing. These surfaces could be paint, fabric texture, or a number of other items. If you have to add surfaces, you can surface the character, like character armor, or you can surface the land. What constitutes sand? What constitutes water? The surface items or their mockups need to be built so they can be acted and filmed, or storyboarded and drawn, or some combination thereof.