They tend to use Recaro or similar seats in big highend sports cruisers. They are really cool, but I don't know if they offer one in some sort of weatherproof version.
Have you seen the Nissan Xterra? They offer an option for pullover NEOPRENE seat covers. Wetsuit material. Perhaps somebody offers those style of covers for sports seats. OR maybe you can find some inexpensively from a wrecked Xterra?