Why make it out of plastic?
You could make one out of wood easily. I think it would look nice too.
You can get oak plywood at the home improvement store. While it won't be quite as nice as teak or mahogany, it's relatively cheap and easy to find. I made new hatch slide rails out of oak on my last boat and they looked and worked great The USS Constitution is made of oak.
Soft woods like pine are unsuitable for marine uses. Don't ask me why, I read it somewhere.
I think it's because they won't hold a screw and suck water like a sponge.
Those grand fresh-water seas of ours - Erie, and Ontario, and Huron, and Superior, and Michigan, - possess an ocean-like expansiveness...They contain round archipelagoes of romantic isles...they have heard the fleet thunderings of naval victories...they know what shipwrecks are, for out of sight of land, however inland, they have drowned full many a midnight ship with all its shrieking crew. --from Moby Dick