Not certain what a Wompus is, but I've successfully mounted trunk(s) to the Triumph sissy bar/luggage rack on my Roadster by not using the sissy bar. Used both the JCWhitney and Bestem trunks. The Bestems a little larger/nicer, IMO the JCW is easier to use.
If you plan to keep the passenger seat I know of no other provider than Triumph to make that happen. If you want a luggage rack in place of the passenger seat a lot of racks designed for 16" rear wheels will work. I.E. the rack from my '02 Victory is a perfect fit.
Hope this helps.