The tank bag is a Fieldsheer Contour bag with the magnetic base. The base slides under the upper fairing, almost like it was designed to do so. It is expandable, which is nice, but I've never had to use it that way yet. The only downside is there is no gas tank access, so you have to pull the magnets off the tank on one side and fold the bag over to fill up, but it's not hard and only takes a second. I use the tank bag more than the trunk. It's easy just to throw my sunglasses, hat, wallet, gloves, and whatever else in the bag and head out.