1. Purchase duvet sheet of sufficient size and 2 cans of spray on glue
2. Take headlining off.
3. Give a quick clean and allow to dry
4. Cut duvet sheet to single sheet, line up to check size
5. Apply glue generously to headlining (not sheet) do this in stages so it does not dry before you have put the whole sheet on, best to use a soft paint roller on the top of the sheet to apply even pressure and ensure the glue does not show through the sheet, if it does it will not disappear as found out

Tommy has some progress pics he could put up if you ask nicely.