Exploring alternatives to make simple cheap rocks to solve issue with transportable crawler feature, came up with newspaper and joint compound.
Like we did in grammar school, paper mache... Sort of like using plaster cloth but this is basically stuff on hand.
Very cost effective, strong and viable alternative. A lot of rambling but the results surprised me enough to motivate & plan an actual coarse instead of my original plan to build individual obstacles.
Large features will still need structure, likely foam packing & cardboard but without expense of plaster cloth and spray foam.