4 gauge jumper cables are cheap. You could just cut the clamps off and then run 4 gauge all the way back and then make your own power station with remote terminals somewhere in the bed. You could still fuse it or add a circuit breaker near the battery.
Just an example:
View attachment 362905
View attachment 362906
I have a circuit breaker on mine with 4 gauge all the way back to the inverter behind the rear seat. And then I ran my fridge wiring (in the bed) from that inverter. So basically, I have full battery power right behind my rear seat and I can turn it on or off via the circuit breaker near the battery.