Has anyone tried fitting a roof box? I've hired one locally from next Saturday but the hire place had never hired/sold one for a Berlingo. I note on the Citroen website the roof boxes shown in the accessories section all seem to say they are not suitable for the Berlingo. Also the roof bars seem only to be rated up to 35KG - while even the smallest Thule box seems rated to 50Kg. Anyone fitted one? Any problems doing so?