I installed my Garauld Gen I Stiffener Kit yesterday, and am quite happy with the results.
I have a Pelican 1520 case on my stock rear rack, and after 40,000 miles or so there is no hint of problems with the rear sub-frame, but I'd like to keep it that way. I drilled four holes through the stock rear rack, and a 12" square plate of 1/8" thick 6061 aluminum mounts with counter-sunk machine screws, washers and rubber isolating spaces, and nylon lock nuts. The Pelican case mounts to the plate with M8 screws, fender washers, and rubber washers into tapped holes in the aluminum plate. Mounting to the stock rear rack seems to have some advantages, because the rack is attached to the rear sub-frame at five widely-spaced points.
I try not to overload the case, but it sometimes happens.
The Stiffener Kit is easy to install. I had some extra work because I had to re-jigger some wiring for an auxiliary LED running/brake light bar. This wiring came through the hole just ahead of the stock left running light. Happily, I was able to re-route it without having to disconnect it.
Garauld provides an instruction sheet with all the steps laid out, and it was easy to follow. You do not need to remove any body plastic -- only the seats need to be removed to access the rear sub-frame area. You'll want a u-joint on your 14mm socket to tighten the bolts that go down through the horizontal sections of the bent plates, to clear the lip of the rear seat mount plastic. Start to finish was about 20 minutes, which included re-routing my extra wiring.
For someone like me who regularly stresses their rear sub-frame, the extra protection provided by Garauld's Stiffener Kit is most welcome. It's another in Garauld's long line of well-engineered, well-built accessories for the FJR.