Profligate that I am I decided the used bag wasn't going to work properly as it is simply too soft and doesn't hold its shape.
Looked at a few Saddlemen options and with my refund from British Airways I bought a new bag.
The quality is instantly evident. It came from a UK Harley dealer and luckily isn't badged HD at all.
It had its first outing on the Somme trip and was perfect it swallowed all our "duds" for the Ceremony and more.
The bright yellow waterproof cover came in handy in some terrible weather and no water got in. The cover is big enough to fit over the main bag and the top back. It looks a bit flimsy but worked well.
At £138 inc taxes and delivery it's not cheap but you'd gave to pay more for hard luggage and a rack to mount it.
The standard setup was the right size for my sissy bar pad and I used two other supplied straps to keep it tightly in place on the little rack, should it try to get off on its own!
The Rocket is so heavy and planted on the road it didn't cause any handling problems as it was probably at the 20lbs capacity and it us behind the rear axle.
I saw a couple of Harleys with no racks with bags not too disimilar mounted the other way around, so the bag was on the back seat. I don't think that will work on the Rocket.