I'm going to use the Happy-Trail racks unless there is some unforseen issue, second would be Hepco & Becker. Caribou uses the HB. They have a quick connect system from the inside of the box, and HT has a screw knob and billet rack tabs that thru-bolt through the case. Twisted Throttle has a very nice quick-connect system that works with SW Motech racks, much like the fancy Givi bags and racks. They just snap on with outside clips and catch. But they only work with motech racks and they won't work on my bike because I have no fender. Or so they told me.
Pelican boxes can also be hard mounted with nuts and bolts as well. I will be using the HT attach hardware pack, it's like $50 and made to fit their racks. I'm sure it's what they use for their aluminum boxes. And they are also offering the pelican boxes now, setup and pre-drilled if you want them.
There are several models/sizes of both pelican hard cases and pelican storm cases that will work on these bikes, depending on how large or compact your aim is. By far the most popular have been the Pelican 1550. I think Twisted Throttle is doing theirs now with the storm iM2600 cases.
My take is if you're loading them with liners or stuff sacks they don't need to come off of the bike. Especially the made to fit inner bags, gear can be easily transported off the bike. Still, a quick release system would be nice for hoteling it, carry them in like luggage. That's what the fancy euro bikes do.
All three of these rack systems come with all the hardware. I think the only one that isn't compatible with the motech topbox rack are the givi and oem kawi ones. The happy-trail ones don't even attach to the same connect points on the bike.
Thumpers bike looks killer, nice setup. And I kind of like the gray cases JDROCKS has on his. I may even consider going that way. But again, since my bike is already all black it may make sense to just get the black boxes to match.
I also have to decide if I'm going to mount the boxes level with the road or even with the seat slope.