Like zzkazu says the trim will come out pretty easily as along the doors it all snaps into place with push in fasteners. There's a .pdf file omn removing trim http://www.wk2jeeps.com/wk2_interior_trim.htm
At the back again its not hard to take out all the stuff to get to the tub so as to get a wire through a grommet.
Big warning though if you remove trim at the rear all the way including the large plastic tub around the spare (that allows the carpet to be lifted) - there are 2 wires into a dinky plug connected to a black box on the tub. This box is an antenna and part of the passive entry canbus system. Remove the wires BUT do not turn the ignition on while removed
. This will spike the canbus and kill the passive entry until codes are cleared and the system reset and reflashed by the dealer. (more on this refer to threads on "key not recognised" on this forum, there's a couple of posts specifically mentioning issues with this).
I purchased a set of plastic trim removal tools from Supercheap that made it really easy to lift the trim along the sides and didn't leave any marks. It didn't need super force so don't just rip.
My advice would be to take controller power from the battery and don't tap into the Jeep system at all.
Except for the brake signal back to the controller from the stop light wire in the trailer wiring loom installed by the dealer