I personally don't use a tank bag. I had one and tended to fill it up with things I "had" to have withing arms reach. It became like my wife's purse. Filled with needless items she can never find when necessary and pounds of "stuff" like an albatross around her neck. Got rid of the bag, shed a few pounds and never went back.
In my opinion, tank bags prove the Vacuum Principle. Empty space attracts items, most unnecessary. Just try it sometime. Clean out a closet and see how long i takes to get cluttered up again! Try not using a tank bag and you might be surprised. It also tends to break up the beautiful lines of the bike.
12 K1600 GTL
02 K1200 LT (gone but not forgotten)