Not having had any satisfactory success, now thinking along the lines of a Top Box Rack.
The Top Case is the BMW 49 litre.
Nippy Normans do this Wunderlich Rack, http://www.nippynormans.com/products/k1 ... -20570-003.

Has anyone had any experience of such items, are they any good & easy to fit, does the Top Case Lid remain waterproof. Any issues with aerodynamics/stability when fitted.
Are there any alternative manufacturers out there which you would recommend.