I don't charge from the truck. I used that hot leg to charge the break away battery. I installed two 6 volt golf cart batteries, and charge up before leaving.
For on site I either carry a Honda 2000 or a 120 watt solar setup. I put an Iota 40 amp converter in that can run off shore/generator that keeps the batteries topped off. Everything is LED, and I've never run out of power even after 4 days.
On the truck side I have a group 31 and 34 AGM Diehards in the front. I ran a 6 circuit Blue Sea accessories box under the hood, and ran another back where the jack is tucked away (8#) for fridge while on the road...but also have a bunch of 12v sockets and USB's. I actually drilled 2 12v sockets in the front fenders if I want to hook the solar in there.
I relocated the trailer plug socket on the truck side to a vertical location by the hitch. Getting too fat and old to fight plugging the trailer in every time. Thats when I got a good look at the wiring going into the rear of the socket. If it's a piece of 18# I'd be surprised. If AT is on the case your in good hands....that's for sure.:ylsmoke: