The optional Porsche covers you can get when you buy a brand new Porsche are all vehicle specific and fit very, very, very well. Did I say very? Because they fit very well. Every Porsche I've delivered has had one of their covers with the car. And owners who know include the covers when they return or sell the cars. None of the ones I've seen are waterproof, just the softest most luxurious material I've ever felt for a car. Not sure if Porsche makes one for a 356.