I ran the wire under the back seat under the side sill and to the headunit, where is your camera located , mines in the keyhole for the trunk i took the lock cylinder out bore out the hole a little bit and it fit perfectly this picture is pretty bad but you get the idea
I believe the easier way is to run it through the A-pillar, along the roof, to C-pillar and to the back. You need to check which side they ran the wires to the back, it will be easier to use the same side. Mine is right hand drive model and they run the wire through the left side.
It is a lot harder to run through the side steps/carpet.