I use relays, a fuse block and circuit breaker in the manner that Cab describes. But, I tow bigger trailers and occasionally not mine trailers.

The not mine ones are usually sketchy and I got tired of losing my truck lights when plugging in.

An isolated system is easy to install. I put my stuff near the battery to limit the length of high Amp wires to the fuse block.

And yes, the factory wires are taxed by extra lights.