Batteries are paralleled to help start the engine, especially when cold and assuming grid heater (diesel) operation. Alternators are also paralleled, useful for trucks with lots of house loads (snowplow, ambulance bodies, pumps, etc). The truck won't charge the batteries in the camper very quickly (any faster than a single alt) due to the 10 ga wiring through the 7-pin - voltage drop across that long of a link will determine your charge rate.
DC-DC charging with dedicated large gauge wiring from the front of the truck to the hitch, and then through a connector to the camper (and using something like a victron controller) would improve charge rate if dictated by your use case. I'm not sure how much the victron 50a controller goes for but #4 (or larger) weld wire isn't cost prohibitive. The controllers are smart enough to detect the voltage rise when the truck is running and charge then.
With that much battery in your camper, it might flatten your truck batteries if left connected when parked if the camper batteries are low. My ram does not isolate with ignition off, but this would be an easy feature to add via a contactor if you needed/wanted it.
