There have been several commercial operators around the country try paint used on grain trailers with some positive results. The product goes under several names a couple of those are "slick plate" and "slip plate". The paint is available in aerosol or brush on and contains graphite, Teflon or some other "slick" material that helps prevent the grass from sticking. Our local TSC (tractor supply) carries it under the "slick plate" name.
The paint doesn't last all year but it should get you through the heavy wet spring season in most regions before it needs re-applied. I had a guy in PA try it last year and had wonderful things to say about it.
I'd recommend using a wire brush on a hand held grinder to get all the rust and debris off the deck before applying. This is a pretty good winter project for a lot of guys when they are getting their equipment ready for the spring cutting season.