Alas, the sticky for the xt225 Clarke tank is hampered by the Photobucket goobering of photos, but the words work. I did update the photos for the xt350 oem tank sticky and the mounting is largely the same . . . so you might benefit from looking at all of the tank sticky threads and being creative.
When I rigged saddlebags for my bike, I used a yoke across the back of the seat to support most of the weight and used side brackets primarily for keeping the bag away from the bike/muffler/rest of frame. I collect rocks in my saddlebags so I know they will hold weight. Enjoy the planning.