Hi and welcome to the forum
What bike have you got
If its a tenere im not too sure, but have a look in the tenere only section im pretty sure ive seen a thread in there someone on tankbags.
If you have an X or an R then have a look at this
http://www.off-the-road.de/5.html?&L=1
ive the one called the tank enduro, fits like a glove, can hold a good amount of gear (13-19litres), is comfy to tour/ride with, and is very strong and generally a good bag.
Downsides are its not 100% waterproof and you dont get a cover to help to keep it water proof, this means your map pocket steams/mists up a bit, the other down side is the map pocket is small i will not even take a full A4 size page which causes problems when trying to find a map to fit(normally either to big or way to small and you cant see roads etc while on the move)
There are a few others out there, try using the search function at the top.