Well.....in that case!lol
I just ran wires for 8 LED rock lights up underneath . There's a gap between the frame and the body ,thats about an inch or two,so I ran them along the frame ,on top.That way it keeps them out of harms way. I cleaned the top of the frame and used a bunch of strips of 2" thick industrial velcro to hold them every 2-3ft ,but you may need to epoxy on some wiring clamps for bigazz wire your size. You would be surprised how much industrial velcro can hold though.
Like I said there are some rubber body plugs that you can take out and run the wires up and in ,then find a way to reseal them .The hard part is taking all the rear inside panels out to access them but it looks like your going to have to do that anyways.
Here's some pics of whats back there and you can see some rubber plugs in the first few shots.
Here are some pics in here of whats under there....
https://picasaweb.google.com/110764526188420500909/InteriorSoundDeadeningWithEDead