I use this bag from Saddlemen:

http://www.motorcycle-superstore.com...-sissy-bar-bag

It has an extension handle and is on wheels so it's versatile and can be used when flying as well. It also has a sleeve which also will fit over more traditional sissy bars. I don't use that of course.

It has a raincover and straps snugly onto the grab handles. I've used it since 2009 on all my trips and it's successfully handled about 15,000+ miles through all kind of weather.