Tapping into rear 12v accessory to charge the trailer

[ferociousllama]

It sounds like the accessory 12v power in the back will work, but I would run a wire of my own. Car manufacturers often times use wire that is way smaller than what is "recommended" by any manual that would tell you an appropriate wire size.

I would take the safe road and run a wire. Then you won't have to worry about any problems because you know the fuse is the right amperage and the wire is the right gauge.

[brian_bp]

Yes, it is possible if you leave some high amp draw accessory on in the trailer you could run the battery's down while parked, But who leaves fans, lights TV's on in there trailer when towing? Not me, I turn everything off before I tow. If nothings on theres no drain.

I run the refrigerator on 12V while towing. It takes signficant current, and could run down the tug's battery if left during a long non-camping stop. It has run down the trailer battery this way...

Well the refrigerator I would be willing to bet uses more power from your battery than your charger is charging the batteries. At least that was the way it was on my pop up.

That could be, but I have not had a problem with running the refrigerator while driving... I've arrived with lots in the battery.

I must admit that I have not checked the battery charge level before and after driving, with or without the refrigerator running.