Not sure if this idea helps but I used to do an awful lot of modifying on cars (was a bit of a boy racer) but I used to do it tastefully and make it look like an OEM type finish. When I wanted to mimic mottled dashboard plastics I used to use stone chip aerosols for the texture. In actual fact (spefically) Hammerite stone chip aerosols used to produce a wonderful fine texture which might do very well as anti-slip texture for decks. I also used to use this as a lazy surface filler primer because when you cut it back it worked much better than proprietary filler primers! The Hammerite cans work great on polystyrene sheets (not EPS obviously!), GRP, wood, metals etc. Might be worth considering? Alternatively, for models I've seen me cut wet and dry paper into the required size and bond it down before painting over.