I just bought a 1977 Excella500 and it had a spray on rock guard. According to the PO he stated that this was an available option that was put on at Airstream. It is a matching gray color and is quite a bit different than the texture of rhino liner or line-x. He had it in his family for 22 years and it was always that way. is there truth to this statement? I have not brought the silver spaceship (as my daughters call it) home yet to really thoroughly investigate.