This mod makes the car VooDoo driveable on the water (not on land tho ).
*note*: you might need a car spawner of any type to get it in the water or you can just jack one driving by.
CarShop V2: http://gtahq.multiplayernetwork.net/file/1261/ (credit to Nikzilla)
To install simply replace files in the archive with the ones in the game.