Old post I know but seemed appropriate place to add this for anyone who is interested.
I have just received a Christmas present for the Tenere. Its a Baglux tank cover, colour matched (not bad either) and a tank bag. Best bit of kit yet. I use ferries a lot and have had damage to the tank from strapping. The cover protects this nicely. I have also tried several tank bags and have as yet not been happy. This is spot on. The only issue is they, Baglux, don't make this bag anymore. For the 'trail' fitting required for the Tenere tank cover you can only get the Tweety (3.5ltrs) and the Cross'r 22 ltrs). The City Trail is 8.5 ltrs and fits without handlebar, ignition key or seat interference.
Thi combination gets my 100% positive vote and recomendation as the best system for the Tenere. �96 for the tank cover and �63 for the tank bag. This tank bag is available if you hunt around some of the smaller dealers who still have it in stock.