That's not the Gigavac product that I was thinking of. They offer one with voltage sensing electronics on-board.
Easier to get is the Blue Seas products. I would look at something like this:
Blue Seas ACR
Anytime you take power off of a battery it needs to be protected with a fuse or a breaker, so you'll need something like this
breaker:
Or this
fuse assembly:
at both batteries or you risk an electrical fire.
This is my camper disconnect:
This is the
wire that I used:
Two of
these make up the disconnect:
(Note that different colors of these connectors will not mate, nor will connectors of different amperage series.)
The socket provided in the bed is mostly for lights. The 7 contact "RV" sockets, which yours likely is, do have a contact for battery charging. However, they are typically limited to a max wire size of 10 gauge. That would be OK for a trickle charge, but it will not carry enough current to do bulk charging without a pretty large voltage drop. Given that the voltage difference between a fully charged battery and a 50% discharged battery is about 0.5 volts, you want to minimize any voltage drop as to as little as possible. Some here probably think my choice of 6 gauge power and ground wires is over-kill, but I wanted as little voltage drop as I could get without adding unnecessary weight. I feel that 6 ga. is sitting on the cusp of becoming excess weight, but I'm confident that the voltage drop is very small.
What connector do you have on the end of your wires that connects into the powerpole??