A. J., I really like that bag - has a very nice look.
I got a 20L Marchway Dry Bag from Amazon and inserted a 19" section of one of those cardboard concrete tubes (8" inside dia) into mine to make it hold its shape.
We then open the end to slide in/out our small snacks,rain liners, thermals, and hat and sunglasses that we access often during the day on our trips.
I have a plastic coated 10" spiral clamp that secures the bag to the luggage rack so no one can do a grab and go on it without some effort. We do take it into the hotel each night or if we have the bike cover with us, we leave it on the bike and it gets covered without any problem.