Does anyone have such a setup?

How did you go about installing the GIVI adaptor bits on an MP3 rack, is there a template?
I was hoping the SW-MOTECH Steel-Rack Adapter Kit for GIVI Monokey Topcase sold by Twisted Throttle for their rack would have the parts necessary to do the job. If there is a better way please let me know.

This all came up because I recently did a 2,000 mile trip and would have liked to bring an extra jacket but just didn't have the room. I have another long trip in the fall and will definitely need some space for colder weather clothing (for on/off the bike-I can leave the swimsuit at home but that does free up much room). I browsed the GIVI web page and like the idea of the big case. I figure I might as well go very big or stay home. It will not be used to carry much weight, mostly to carry my spare jacket, rain gear and some other light stuff.

Thanks in advance for the help/advice.