Since it was the end of the camping season for me, I put off solving this problem until now. I bought a WFCO 9835 converter and I'm ready to wire it in.
On the 12V side, this WFCO has a positive and negative jack, and a ground screw. I'd like to mount the converter inside the trailer, against the front wall near the AC breaker box. The battery is mounted nearby inside a vented box, and the pos/neg wires run through the floor and inside a plastic wire loom to a water-tight electrical box. Also connected to this box is a set of wrapped wires that runs to the trailer 7-pin jack at the hitch, and another set of wires that presumably run through the trailer walls to the lights and 12VDC power points. Here's a picture of underneath the trailer:
(The ridged wire loom running across the underside of the box are the battery cables.)
I had attached the Battery Tender Plus directly to the battery posts.
Is it enough to remove the BTP and attach the BTP's red/black cables to the WFCO? What about the WFCO's ground screw? Or something completely different?
I expect to have an electrician install a fourth AC circuit breaker and circuit into the panel and install another 110V jack under the counter near the panel to plug the converter into.
As always, thanks for any advice. -Gary