Do you have a sissy bar that will fit it? Best thing is to get a roll bag like a duffel bag but shorter and wider and with a zipper, and strap it to the inside of a sissy bar so it also becomes a back rest. I think they are big gym bags. I have a big bunch of amazing army surplus straps that are about 2' long with a clip on one end like a big alligator clip the width of the strap, and plain on the other end. You can combine them to make longer straps. They cinch down real tight. Real glad I stumbled onto those back when.
exactly what I do a kitbag can also carry a load of useful stuff.
It might look a bit uncool easy rider but my back sure thanks me for it.