A few pics of the panniers and top case for the HP2e system described above might help, eh?
These are "stock" photos of the Holan natural/aluminum panniers and the 29L top case included in the system. I'll get exact measurements from Holan, but the system looks to be nice and narrow (31L panniers are approximately 8" wide; 38L shown here are about 9.5"). Also, just to clarify, due to weight restrictions on the BMW, you can either run the panniers or
the side cases, but not both simultaneously. Use the panniers to carry gear for your big trip, then dump the side cases and run the top case for urban assault duty with the narrowest profile.
Holan Nomada Pro 29L Medium Top Case -
Holan Nomada Pro 31L Panniers (Natural/Aluminum) -
38L cases shown; the 31L cases are approximately 1.5" narrower. Lower tie-down foot loops at the bottom of the case are not included but can be ordered/added separately.