It involves taking the real sand covered (queen-size) sheet and draping it over very large crumpled rolls of paper free from the factory bin out back. (seen in diagram below, pipe on back wall is electrical conduit for scale.)
An easy solution to create more terrain will be to use more paper to establish the dune shapes and then cover them with matching thin foam sheets or inexpensive fabric dyed to match the sand. I also feel the real sand needs to be stained from the natural color to bright golden yellow with a bit of gold leaf flecks in the close-up areas.
The material used for the background hills will be made to match the final sand color, rolled under at the edges and fluffed into shape. Should blend well enough, especially for the blurred background.
The desert set was always planned to be placed in front of the same infinity sky scrim built for the main cottage set. If I position the desert at an angle, I may be able to fit it in without having to dismantle the main landscape much. If not, I can always take the desert set outdoors and shoot there. It's a very portable set as the sands can shift as they like, as real sand does, won't matter in this film and may even add a nice montage effect. Even the sun light moving at the "wrong" frame rate may enhance the surreal effect of these particular scenes.
Should take place bathed in strong end-of-day golden sunlit glow though.Will play off the gold nicely.