I have the Triumph high passenger backrest with luggage rack. I purchased one of those expandable bags that rests on the luggage rack and has a couple of 3" wide velcro straps that go around the sissy bar to hold it down. It has worked out very good. In there I have a half helmet, a medium weight jacket, rain gear, and gloves. You just fold the top over and over making it shrink in size or expand.
It's not perfect but it cost me about 90 bucks and it works.

jerry

2005 America, Green, Thunderbike exhaust LEAD, FOLLOW, OR GET THE HE** OUT OF THE WAY!