My new bike came from the showroom with a sissybar/rack combo attached. To install my trunk, I just sawed the backrest part of the rack off, which left me with a nice smooth rear rack only.
You can do that, or you can remove your rear seat and install a trunk to the top of the rear fender.
I would suggest hard luggage over soft, but that's just me.
This isn't the best photo of my trunk, but I'm in the office and it's all I've got.
