With two batteries in parallel, you should need only one disconnect switch in the ground cable side. I had a switch on our 2016 Parkliner
, but just one battery, so was able to locate id in the empty space where the second battery would go.
Unfortunately, after a couple of winters, the switch would stick in the closed position (it had a spring inside the was supposed to open the contacts when the key is removed) As a result, I had a dead and frozen battery again.
There was a trickle discharge because the CO/LP gas detector was always energized. Now, I have a small "light" switch behind the detector to shut it off when we're not using the camper.
Send me your e-mail, and I can show you pictures. Lwgcollins@aol.com