An article on Brown paper covering on foam models was written by Chris Golds in Radio Control Models & Electronics July 1982 page 628 ( published in England by MAP -now called Highbury )
Another article by Chris Golds in RCME published in May 1983 page 379 showed the technique on his 90 inch span Lancaster plan No RC 1457

Chris mentions using Borden PVA and thinning with 30 % water and some red poster paint (artists paint ) to colour the glue. He advises putting PVA glue on both the foam and the brown paper. Also sealing the outside of the brown paper with thinned PVA to make a good surface for paint