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Aggi's link isn't what's in the picture...
You're better looking at something like the Wildcat saddlebags from what you're describing: http://www.wildcatgear.co.uk/products/seat-packs/
I'm not sure who makes the one pictures, maybe Archies or BRP (I know the latter BRP ones had a removable dry bag e.g. http://www.englishcycles.com/wp-content/uploads/2013/02/gates2.jpg)
@atk started
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^
Aggi's link isn't what's in the picture...
You're better looking at something like the Wildcat saddlebags from what you're describing: http://www.wildcatgear.co.uk/products/seat-packs/
I'm not sure who makes the one pictures, maybe Archies or BRP (I know the latter BRP ones had a removable dry bag e.g. http://www.englishcycles.com/wp-content/uploads/2013/02/gates2.jpg)