When I got the Wee, I really wanted the Caribou cases and no top box at all. I got lucky and found one with Pelican cases mounted to Givi racks, but also a Givi top box (which was easy to remove). After I realized that the Pelican's on Givi racks wound up making the Wee significantly wider than my ST1100, I took them off and rode around with no luggage at all. I really liked the handling of the Wee without luggage a lot, but I missed having a place to toss a few random things. I decided that I wanted a top box, but I didn't want to use the Givi since they don't quite fit the look of the bike.
I decided that one of the 1550's would make a great top box, be narrow enough for the bike and short enough not to look too odd (in my opinion) on the back. I removed the rubber pad on the rear rack and used the center hole and the two back holes in that rack for directly bolting the Pelican to it. It seemed a little floppy, so I took a piece of 1/8" thick aluminum plate that I had and cut it approximately 5" wide and 9" long and put that on the same bolt holes, but sticking off of the back of the rack to give the Pelican some support on the underside. It works beautifully, leaves plenty of room for a passenger (that I never intend on riding with me), and is unobtrusive. I think I'll add soft luggage if I ever want to do a trip on the Wee, but for normal riding the top box is all it will see.
A couple small things left to do still. I need to perform a fenderectomy now and I need to design a tie-down rack that mounts to the top of the top box.