Have that same tail pack. Used it on my ninja 650 and my other day bikes. Love how it doubles in size when you have to shed layers.
It is a great tail pack. We started with it not expanded, but after trying to stuff things into it, I expanded it and it was so much easier. I don't think my wife had seen to expanded.
I need to get a new rain cover for it. Mine blew off somewhere in Ohio one day. Now I just put a trash bag inside. The bag itself does a decent job keeping water out, but the rain cover helps a lot.