I use the Sargent Superbag system. (
www.sargentcycles.com). It works well for me, is extremely versatile, and, even though it's a strap-on system, doesn't shift. It's easy to flip over for refueling. I have the Triumph bag on my Legend, and find the Sargent bag is a little large capacity (in actual use) and doesn't block as much of my guages. Remember, the Triumph bag is also a strap-on system.