I bought one for my 5 by chance just this week,saw a
car on ebay,noticed it had a tonneau cover,so i emailed him and he agreed to sell it me,£60,and to be honest it is mint..noticed he hasn't changed his listing,so to who ever gets his car the tonneau cover is on mine
Saw that one on ebay,he says its not for a 5,and i thought the 6 tonneau was more "bulbous" than that,and i think the gen 4 tonneau is more flexible leather/vinyl type....could be wrong though,it might be for a 6.
Must say though if you can find one i would recommend it.....they make a huge improvement to the look of the car.