Trunks come in a variety of makes, sizes, prices and shapes, BUT, they all fall into only two categories when it comes to mounting them to the stock rack or an after-market rack.
(1) Only Givi monoKEY trunks can be attached directly to an after-market rack using either Givi or SW-Motech mounting kits. (I'll contradict myself by saying, JC-Whitney / Sears may sometimes fit).
(2) All other brand trunks will need a universal mounting plate that usually comes with the trunk. The universal mounting plate can be attached to the stock rack. This includes the Kawasaki trunk often sold with the bikes.
There are advantages to both methods of attachment, The monoKEY fits snugly and securely with minimal "bobble" but, unless the rack is adjustable, it's in a fixed location.
All other brands using a universal mounting plate offer some degree of adjustability in positioning them on the rack, but at the price of another layer of plastic between the bike & trunk.
I hope this information helps people before they but a trunk and are then disapointed in their mounting options.