HI Keith
If you get some tissue paper , cut it to the size you want then soak it in a mix of water and pva glue (white school glue

) a mix of about 50/50 does fine.
Place it over the area you wish to cover and mould it to shape, you may wish to add creases and folds at this time as it will dry quite hard.
Leave it over night then you can paint it , drybrush it etc.
Take a peek at my gallery , theres a tarp over the back of my cromwell i made using the above method
Ian