[Water Warrior 2]

Give a little more thought to the hard case on Alantf's bike. I have the same case. It comes off in a second or 2 and you carry it like a suit case. Water proof and tough as nails. More costly than textile/fabric bags but they are lockable and very secure on the bike. The Shad brand which Alantf has comes with it's own mounting plate for a rack on the bike. There are a few options for a rear rack but you can always try to make your own.
I took the easy way out with Lynda's GZ and mounted a top case in place of the pillion seat. I made up a steel plate to serve as a mounting rack with the top case mounting plate attached to it. Worked great and she had a backrest to boot. Lynda never carried a pillion so everything worked out perfectly.