Don't mean to hijack, but how does connecting a house battery in this manner differ from using battery isolator set up?

 

Functionally, I don't think there is a difference.

The advantage though to using the trailer plug connection is that its already there and wired with relays. So, no added parts or labor. Just run a wire to the pin in the trailer plug or tap into the wire thats under the bumper.

 

One way uses a relay, the other uses power diodes.

The difference is what is known as a "junction voltage" drop.

Wish I had time to explain it all this afternoon, but Google is your friend!

Pop

 

I always use relays for isolating house batteries.
Those diode based isolators tend to eat a volt in my experience.