Now that I'm retired my luggage requirements are best described by the words infrequent and minimal. Then I did something a younger me would never have even considered. Shop for a tail trunk! Why? Because high up and way beyond the rear axle is the absolute worst place to put additional weight or a big draft catching box. It can dramatically alter/harm the stability of a bike.
Tail trunk size was the most important. I wanted small. Found just what I needed in the Givi E260N. It was also $116 delivered to my door!! Here's what it looks like installed:
Adapter plate installation, my way
rear view
left front view
left rear view
Right center view
The case is sized and meant for scooters, but holds my full face Shoei helmet with almost an inch on top to spare. There is a 3 red LED brakelite kit and backrest pad available, but they are too expensive for what they are. Both can be created by the owner with careful planning and readily available parts/materials.The case removes with the key and a single button press. The case installs with the key and just tucking in the 2 front lugs then pressing the case into place with a loud CLICK. 10 seconds tops for remove or replace!
FYI: The supplied bolts and brackets did not guarantee the rack would be accurately located or securely restrained. Toss that! Looking it over, the many holes in the plastic adapter plate determined where the screws could go by the BMW rack showing thru 6 of them when the plate was located where it needed to be. Those 6 logically placed screws and 1 bolt securing the adapter plate to the BMW rack creates an incredibly rigid mounting that will never loosen, is practically invisible on inspection, has greater security against someone with simple tools and provides 7 as opposed to the default 4 attachment points. That shares the road shock load and high speed wind forces over 7 rather than 4 areas of the somewhat thin plastic framework, enhancing peace of mind it'll always be back there. Drilling and taping the six 5mm x .8mm threaded holes in the BMW rack's soft Aluminum requires patience and good vertical alignment. Surprisingly, riding the bike with or without the tail trunk attached feels the same. The lid outer sealing edge goes down over the inner bottom edge by about a half inch, without a gasket, so it very likely will not be 100% water tight in the breeze. The case does not show in the mirrors until I turn or tilt over sideways. It is almost always attached to the bike.
Money very well spent.
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below:
Note the male and female terminals that mount to the case floor and to the exact mating location on the adapter plate. They electrically connect the case's brake light LEDs to the bike power as you snap the case into place. For about $12 worth of LEDs, a resistor and 2 mating terminals from "the Shack" I can make an equally functional, trouble free, super bright LED system. With 2 blocking diodes and an additional higher Ohm resistor there can also be a half brightness running light using those same 3 LEDs. The very low additional power draw of those 3 LEDs does not trigger any reaction from the BMS-K main computer. 
