The official Zero top rack arrived with the
Givi E340 Monolock top case. Installation took just a couple of allen wrenches (5mm to get the seat bolts off, 4mm for the rack mount bolts, 5mm again to mount the monolock plate) and additionally a wrench and screwdriver for the monolock plate mount.
I spent about 20 minutes total on the installation, rather leisurely, really. I suppose my one point of confusion which the instructions didn't clarify was whether the rubber-bumpered part of the tail mount went over or under the end of the tail. I placed it on top for the ride home but it seemed slightly wrong. Pictures attached show what I mean.
EDIT: I re-examined it close up, and it's clearly meant to rest on the tail and not under it, given the angle of the bracket for that rubber bumper. Also, the bars don't admit any upward motion so I don't feel like there's a danger of it "lifting" off of the tail. So I'm leaving it as-is unless I get official advice otherwise.