Brandandfox, if you want hardsided tragkorbs on the K-bike, you are gonna need the mounting hardware. The link I posted is just that. If you have the mounting hardware, then you can fit the tragkorbs. I happen to like the Hepco Becker Junior bags. The are sorta the plane vanilla models of the HB tragkorbs. Other models are a bit sexier. The Juniors are not perfect, but what in life is?
They are available in 30 and 40 liter sizes - maybe even larger but I'm not certain on that point. A nice feature of these particular tragkorbs is they can easily be mounted on HB racks or the BMW OEM racks found on the airheads.
Versatility is good!