I used marine grade vinyl in my boat and love it so much more than carpet!
It has a non-slip finish, sheds water instead of absorbing it, is a heck of a lot easier to clean, and looks good too. It is also less $$$ than most marine grade carpet too.
I looked around a lot and ended up buying my carpet from a vendor on ebay. I paid $4.99 per linear foot for a 6ft roll. I am very happy with the carpet. It is marine carpet with a rubber backing and is very nice. Also received the carpet very fast after ordering. This is not much more expensive than the cheap carpet that Lowes or Home Depot carries and it is actual marine carpet that is not the loop style like most of the cheap carpet that I have seen at these stores. If you are interested let me know, and I can get you the name of the company I ordered from.
Well, I decided to go take a look at the Home Depot by my work during my lunch break, just to see what outdoor carpets they had. I found the following carpet in pre-cut rolls and it was marked down to more than half the original price. I had to take a roll. I bought a 6' x 12' roll for fifteen and some change. I think this should work fine to cover the plywood on my bench seats. What do you all think?