I was looking at a bag that attaches to the fuel cap area. It might put the bag too far to the rear. A standard Triumph fuel cap mount will work.
https://www.revzilla.com/motorcycle/givi-st602-sport-t-tanklock-4l-tank-bag?gclsrc=aw.ds&&gclid=Cj0KCQjwrfvsBRD7ARIsAKuDvMMogUtrE_1d2352nnaDgspTTRKAaeChPJrq9GlBvoVE-Nc1yL0SWJcaAualEALw_wcB