When I bought my ST it came with a tank bag. The bag is fairly large and a touring bike may not leave too much room over the tank with lock steering:
I don't know why full lock gives about a foot of room over the gas cap because compare steering to a sportbike. A tank bag has little effect on turning radius due to the handlebar position and full lock is not nearly as troublesome:
I have tried to use a tank bag but the space conflict is concerning: steering lock reduced and controls may hit the bag as mine do. Once counter-steering takes place at speed steering lock is not unimportant; however, the last thing anyone needs is a horn, starter switch, turn signal or other electronic wizardry hitting a bag while doing a slow tight turn.
What's your opinion on tank bags on sport tourers, does there have to be a compromise? I know the storage is not needed but carrying maps/water/food/electronics/W.H.Y. on the tank is much more convenient than locked luggage. There's the option of fabricating a guard over the controls but that seems hokey.
I am looking for something to carry a hydration bladder in for a trip next month and trying to replace this. I am trying to find a bag to carry a gallon of water but with room I have it doesn't seem to exist.