Thanks, great advice! I couldnt find the original thread so I thought I'd say it here.
Tried it today and it makes a HUGE difference, usually the salmon slide all over the top of the transom fish box top while trying to clean them and its a big pita. As soon as the fish slime hit the cuttingboard plastic lid it was worse than being greased.
Today it was like they were velcrod in place, I see what you mean about getting the short blades of plastic grass though, took a while to get it clean with the deck washdown nozzle.