GPS installation

[Allensr]

I'm getting ready to install my Garnin 660 on to the STS handlebar. Where is the best place to get the 12 volts from? I'm using the "always on" fuse for my 12 volt outlet, should I use the ignition switched fuse for the GPS? What is the best way to route the wires? How much plastic do I need to remove. I also want to install a 12 volt connection under the seat for heated clothing, any thoughts or suggestions?
Allen