Running 12v to the back of vehicle

Hi

I am wanting to run 12v power to the back of my vehicle. Ideally, I will have a plug in the boot to run devices (like a fridge and/or recharge a battery unit) and another next to my towbar so I can plug the trailer into it and run a fridge or whatever in the trailer when we are on the move.

I was planning on using Anderson plugs and #8 B&S cable, but I am not sure what to do at the engine-bay end. Do I just use a 20 or 30 amp circuit breaker or do I need a relay? (someone told me I did). Narva make a nifty little relay that takes a blade fuse, but instead of using a blade fuse they have a mini-breaker that goes into the aperture the fuse normally goes into.

The car does have a 30A power feed going to the rear from factory, which is always hot, but after pulling all the boot lining away on the weekend and seeing this wire for myself, the gauge of it is way too light in my view to handle that sort of current over an extended period. It's pretty small.

Any advice or pointers would be great, thanks.