I just recently received my Wet Okole Seat Covers. The seat covers are neoprene and 100% waterproof. They fit nicely and add a little extra cushion as well.
The Wet Okoles are pricey. Just for the two front seats on my Frontier it was a little under $300. If it wasn't for my wife getting it for me as an early Christmas Gift, a towel under my butt would have been good enough.
http://www.wetokole.com/
