I installed the Kenwood CMOS-310 recently in the 09 handle. I just lined it up inside the handle and used the two screw holes in the back of the handle to secure it in place with a piece of aluminium. I then packed it with silicone to keep it in place. If you pop off the plastic foot trim in side the rear left door, you will see a hole that has a black plastic plug on it. I ran my wires through this hole and secured it under the bed with tiewraps. From inside run the wires under the foot trim inside the drivers door and up front. Buy 14' of 1/4" wire wrap for under the bed and bring it up in the lower left tailgate corner.
PS consider the $10 DIY tailgate lock at the same time and the wires will run together. See post 89 by Nuke83
http://www.ridgelineownersclub.com/forums/showthread.php?t=9981&page=9