With the bike in storage, winter months are great for research. There are lots of reviews of luggage for the GPz available online. An excellent summary is available via the GPz Mailing List page. The Givi system seemed the right choice. It’s true hard luggage, quite waterproof, easy to remove, and comes as a very flexible system of components. I ordered two E-360 side bags and an E-460 top bag, with the 3-bag wingrack and tail lights. Special mounting kits, specifically set up for most touring bikes, are available, and I ordered the one for the GPz.
Installation took several hours, but was straight forward. I kept a photo journal of the installation process.