Here is what prompted me to start this project. This is what I got from GIVI, it's their PLXR quick detachable brackets for the VFR-X. You can see its either the wrong set of brackets or the design is flawed. There is no way that bracket holder can be forced onto the side rails without damaging them. If they were forced on they'd never come off without doing more damage. Applying lubricant doesn't work. Then, you'll notice the side rails on the bike are curved whereas the holding brackets are flat. What would happen is that the bracket holders would wear on the side rails and after removing them (if you ever get them on) your bike looks like someone went after it with a grinder.

So following the post for the top case project, I'll go after this step by step. One objective will be that the brackets will be removable with as few pieces as possible and that when removed it will be as if they were never mounted, no scratches or worn areas.
The materials list is as follows:
A 12"x12" piece of carbon fiber cloth. You can use fiberglass mat too.
Epoxy
paper measuring cups (small) and some stirring sticks
small chip brushes
an old spoon
5/8" ABS (a 12"x12" piece should be sufficient.
1/8"x2"x30" piece of 6061 or 7075 Aluminum (6061 works just fine as is easier to use but 7075 is better if you use case is extreme conditions) Just note that if you go with 7075 that it is much harder to cut using a hand saw. This application doesn't need it and any force that will break it or bend it will have already caused colossal damage to your bike.
Assortment of 1/8, 1/4 or M4 and M6 screws, nuts and washers
The tools you'll need are the same as those used to make the top case rack in the other post. Add some nitrile or latex gloves though as when you work with the carbon fiber sometimes the epoxy will get on you hands and it's messy.
Don't be put off by the carbon fiber and epoxy aspect of this project. When you see how it's being used you'll see that we aren't making boats or high end wheels but adding some strength to areas that should never need it so it's a fail-safe sort of thing.
As with the topcase platform, I'll go at this step by step, a little each day so if you decide to follow along you can and when I'm done you will be as well.
I highly recommend that you not buy the aluminum or ABS until we get into a few steps so that you can have close measurements and not buy too much. Since we'll cut the aluminum, sometimes you can source end cuts from a metal supply shop and getting a few shorter pieces than one longer one can help. Often you can get the pieces you'll need for very little $$ or free if you ask nicely.
On the type of side cases you can use, it's really up to you. The easiest kind to adapt will be those with a flat inner side but you can also use those cases that bulge to the inner side, the adapter plates will be needed and we'll go over that. Flat sides cases (inner side) can be mounted using very simple adapter plates. You can make up different adapter plates for different side case and swap them as needed.
If you like soft side bags, the bracket we'll make is perfect for that. It will stop the bags from flailing around and protect them from road grime slug off the rear tire.