Check out this story by 5ftinf on @stellerstories www.mytimefriends.com loves this!
Cardboard christmas trees Más
Journey Off the Map - Colored Paper Decorations
I did this last year and it worked great!!! Not a whole lot of work either. I just used a foam ice chest and made a frame with chicken wire and paper mache to fit right over it. If time is an issue perhaps a prefab rock like evil eyes suggested would be even better!! This is how the rocks turned out
Creative Construction: How to make a cave out of paper
How to make fake rocks with concrete. Good for covering eyesores. Watch the video at the bottom of the page.