Vic Balshaw
Major General
Though it might be difficult in your scale(or not), I've read about mixing white glue with water, wetting a tissue with said substance, draping it over a former until dry and then cutting to final shape. I've never used the process but have seen some very nice results in model magazines, ie; tarpaulins draped over uncovered engines and covers for tank storage bins.
Geo
Now that sound feasible George though one would have to smooth the tissue fibre down for a bed sheet. Worth a try though Michael.