I've just purchased a reynolds rack with backrest for my K, and am trying to figure out what to mount on it. I'm thinking i'd like to have a hard and lockable box on the back, and only mount the rack for long tours. Can someone recommend a box to mount on it? I'd like to find something that maximizes space, and maybe dips down on either side of the rack...sort of like a hard version of the revpack tour pack. Thanks for any advice!