Can't remember what I bought but it was an aftermarket unit. Just make sure it has rubber gaskets and washers in the 4 posts that go through the lid. It is flimsy plastic. Mine is full with rain gear, scarf, jacket liner and misc things like electrolite packets for water, kleenex, etc. Not one problem.
In fact, after a cross country trip, I never bothered to take the Kuryakin bag off. It's still there and still packed. No issues.