Here is the answer to your problem!!
I have a 2003 Trophy. I wanted a tank bag as I was going on a European trip. I saw bags at crazy money....until I went to Lidl. I bought a bag with magnets on the bottom, it was expandable depending on how much I wanted to fit into it. It had straps too but I didn't use them at all. The fairing on a trophy gives almost 100% protection to anything sitting on the tank. And the bag cost £14 !!! (which also included a waterproof cover!).
"Life is too short to drink cheap wine!"