I read through this and thought I might share a same story.
I recently fitted exactly a similar setup in a poptop Caravan for one of my customer.
We setup with front Anderson plug to charge through 20a dual battery charger, and another Anderson plug on the side of the caravan for solar charger plug. We also setup behind a 2000W power converter and an array of extra accessories, USB, lights.
It was not working at first then quickly I tested the battery was too old and low. So they changed a new FullRiver 105ah and great ever since.
So if your system does not work, assuming you have 12V+ charging from the car to the caravan either from original port or a direct Anderson plug from the front battery, likely the problem stays at the Dual battery charger unit or your battery.
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