We just finished up Seussical at the Melrose Middle School (MA, USA). The set was a pair of large wagons decorated with painted cardboard cutouts. One side was Whoville and the other was the Jungle of Nool. All of the paint used was was mixed with flame retardant, but we never tested it for flammability.  Most of the cardboard elements are available if you are close enough to pick them up. We are taking offers. I have placed pictures on line at http://techshop.net/shows/Seussical/