I would suggest if you buy or make one, use one that stores the tour pack horizontally (like it sits on the bike). I did not... I have one that is stable and works like a charm... with one exception. The tour pack hangs vertically, with the tail light end up and the backrest end is down. I've noticed storing it in this orientation is causing the liner to sag away from the side in the rear. I think it is caused by the weight of the pouch that holds the owners manual and such that is attached to the liner along the back wall of the tour pack. It's not that big a deal, just something I noticed and thought I'd mention it... If I had thought about it before I would have probably went with a horizontal rack instead.., just food for thought. I used a rack built like this.
My take is....this is for people that have a lot of excess cash and don't know where to spend it any more......mine sits on a rack in the garage covered with a Mink blanket......
2"x3" slotted angle, threaded rod, and aluminum tubing to fit the racks mounting points. Mounted to studs on wall, threaded rod through with tubing between the angles, mounted at appropriate spacing and the back rest/luggage rack are on the wall out of the way. Wish I could take and post photos, but don't know how!!! But this is a cheap and easy way to mount up out of the way. Don't have a tour pack, but it would go there too!!!