From time to time I do art work for the National (primary) School here in town. The Féile Scoil Drámaíochta (School Drama Festival) was coming up and they needed props. This year I was fortunate to have large cardboard packaging boxes to use as backgrounds that can stand on their own. I don't know how to describe the boxes. They had Kodak labels on them and were about the size of A1 sheets, maybe bigger (at least 4ft x 3ft and thin when closed up properly). The school has access to a resource centre in Castlebar which often has these handy boxes as well as paper and other strange bits and bobs.
