There was an article in the 1980s in Radio Control Models and Electronics (English mag ) on covering a foam model of a Lancaster in brown paper and white glue by Chris Gold ( a well known modeller in England )

It is an excellent technique. The brown paper used is the type that is shiny on one side.The Pva glue is slightly diluted with water and some food colouring dye can be used to show where it is applied. After applying the brown paper to the foam the paper is coated with glue on the outside which dries to a hard shell. Foam components are then more like balsa in appearance and feel.
You can also cover foam wings with tissue and dilute PVA ( or use wallpaper paste diluted ) instead of using dope which could penetrate into the foam. Obviously you still need veneer or balsa covering too unless the wing has been designed with spars!
Try the techniques on some scrap material first.