I had made one strapped to a Dan Vesel luggage guard, but had to give that up when I decided to use hard cases. I don't intend to keep the hard cases on the bike all the time, and was really missing the extra storage - I can keep my Frogg Toggs in the tube.
I was intrigued with the idea of using the SW-Motech quick-release side rack mounts I had put on for the hard cases. So I took some of the scrap steel I have and started cutting, bending, drilling, welding and painting. I came up with a rack that fits onto the top two quick-release mounts. While it was pretty secure, the tube could still wiggle quite a bit, so I added a third mounting point. The third point uses the rear fender bolt, which I replaced with a longer stud and secure with a wingnut and lock washer. The tube is secured to the rack with 5" stainless steel hose clamps. I had purchase locking quick-release bolts for the side-racks, so I had two extra quick-release bolts I'm using for the tube rack.
Here's the tube with the rack showing:
Here's the three mounting points:
Here's the tube on the bike:
I didn't try to get the tube to match the look of another exhaust system, so it looks asymmetrical from the rear. But I like the side view as the tube parallels the bodywork line.