So I bit the bullet and got some hard sidecases. The SW-Motech quicklock sideracks are the cat's meow. 4 half-turn fasteners and the rack comes off.
I debated several different cases, but couldn't bring myself to shell out $500 for Givi's. You may have seen the post with the Pelican deal on e-bay. I got two of the 1520s that show no signs of use for about $130 shipped.
Rather than spending the money (do you see a trend yet?) for a Caribou mounting kit to be able to pull the cases off easily, I bolted the cases directly to the sideracks. I can still remove the rack and case together in 15 seconds or so, and the racks are not very bulky. I don't forsee the need for removal and transport of the cases too often, so I bet the racks don't get in my way. At least not several hundred dollars worth anyway!
I use 4 stainless steel 1/4x1.5" shouldered bolts, 4 1.5" fender washers on the inside with a bead of rtv on the backside, 4 .5" stainless washers and locknuts with loctite on the backside. Installation was simple, but it took an hour or so to whittle down the ridge and the feet that are molded in to the back of the Pelicans. I could have left them, but I liked the idea of mounting the racks flush to the boxes.
So for less than $400, I've got a pretty sweet setup if you ask me. Take a look...