As I have posted before, wiring a rear mounted winch should be done very carefully.
I have seen two fires caused by liftgate wiring.
The first, was after it had been on there for several years.
Chaffing and wear caused the wire to short to and weld to the frame.
The second, was just pure stupidity. The shop that installed the gate, a major shop that does dozens or more yearly, actually attached the main power cable to the exhaust pipe!!
Not close to the manifold, but it still got hot enough to melt the insulation.
The only two times I have run a rear battery cable, I ran it inside schedule 80 pvc pipe.
80 was overkill, of course, but I had some handy. I clamped the pipe to the frame very well, greased the wire and pulled it though.