I've managed to do something similar. Dealer inspected the damage, and has suggested two possible fixes. (My rail is made up of two lengths with the join just about half way along the roof). First option is to replace the complete rear half section, or, alternatively, cut the damaged rail at about six feet above the ground, just above "eye-level", and only replace that part. My 'vans quite new, so I've opted for the first option, but wont be getting it done until after the hols.