I don't see it mentioned yet or him chiming in, but I think what Phil Bleazey did is absolutely top notch. Hell it's even cobbled together from the frame of an old electric branch chipper.
Unobtrusive, quickly removable, doesn't take up much room when stowed somewhere, and looks fantastic loaded with Craven Golden Arrows that you can still acquire from Craven. Best part is with the top box locked in place it prevents the lowers from being removed.
I couldn't find the thread where he mentioned this and I recall stumbling upon on it when viewing his site, so Phil, please feel free to link any relevant information here, I just thought it was worth mentioning as this is by far the best I've seen luggage done on a M3W