There should be a lot of threads on the forum that will help you do this since a lot of forum members have installed GPS on their bikes. Here's a link to Boneman's website which should get you started.
I'm in the same boat. There are threads discussing this and some good how to's. If you do a search in the Mods and/or How To's you should find something that will guide you or give you an idea.
For me adding the 12v outlet is not the problem. It's where and how to mount the gps in a sturdy manner.