The basic idea is to provide an attachment point on the underside of the case for the nylon loop end of a Rok Strap (I use the non-stretch end for this attachment point) The other short "stretchy" end of the Rok Strap is looped over the pannier support frame that provide the upper mounts of the side cases. The end result is that the luggage being secured is centered over the top of the side case. The problem this solves is most relevant for riding two-up when you have gear (like a tent, etc.) that won't fit in the panniers or top case. WIth this mounting scheme, the passenger can still grab onto the hand holds for security, which is difficult or impossible if you secure this kind of luggage only to the side case frame with straps because it pulls the gear tight against the frame and seat, thus limiting access to the hand holds. There are other schemes using Bungie Buddies mounted on the side cases to accomplish a similar result, but they require drilling holes in the side cases; also, getting two of them in the right position on the outer lid didn't seem possible to me.
The strategy here is to use a flat plate, with a slot for the nylon strap loop, that mounts to the lower outer half of the side case using the two screws that mount the hinges. Here is a mechanical drawing of the plate. The dimensions are in inches, with mm dimensions given in parentheses. The plates I made are 1/16" thick stainless steel, but thicker aluminum would also work. Two plates are needed for each side case:
You remove the two 5mm screws that hold the hinge on the outer lid of the side case and mount the plate under the screw heads as shown below:
The nylon loop of the Rok Strap attached to the mounted bracket looks like this:
Note that to make it easier to install the Rok Strap lower loops on the brackets, use a razor blade or seam stripper to cut the threads of the seam that produces the "curl" on the nylon loop. This will turn the end back into a "flat" loop with minimal thickness that is easier to slide through the slot on the bracket. For the upper attachment, loop the stretchy short end of the Rok Straps around the support frame for the side cases just behind the "pedestals" that slip into the receptacles on the cases. On my bike, I have the frames that also mount a rear luggage rack and, when looped over the frame, it looks like this:
So far I am very pleased with how these work. If you ride solo exclusively, don't bother with this modification, as it is just easier and more secure to mount a large bag transverse on the passenger seat behind the rider with Rok Straps around the pannier frame. But if you ride two up sometimes, and your passenger likes the security of those hand holds, then this system provides a solution.
