Update: I mounted the camera on the bottom of the bumper.



Ran the wiring through flexible plastic mill conduit and zip tied it to the trailer wiring. The rubber grommet entering the body is under the driver's side cargo tie-down ring panel near the tailgate. The grommet pulls out easily, so I used an Xacto knife to slice a small slit in the grommet and fed through the conduit. If you keep the opening small enough, it's tight against the conduit but I used some sealer to be on the safe side.

This got me into the driver's side tail light cubby where I tapped the red/yellow (reverse) and black/white ground and plugged in the previously routed video cable. Done!