Our Mobile Suites is equipped with a residential fridge, 2 each 6VDC batteries and a 1500 watt PSW inverter. We've traveled 12 hours many times and have never had a problem with fridge operation or battery discharge - the Ram does indeed charge the MS coach batteries through pin #4 of the Pollak 7-pin trailer receptacle on the truck.
I can't speak to overnighting, but with the fridge already cold, I don't know how much the compressor would run just to maintain temperature for 8 hours or so if the doors of the fridge stayed closed. For boondocking, you would need more batteries, lots of solar and/or a generator.
We're very pleased with the residential fridge after the troublesome, unreliable Dometics and Norcolds we lived with for 20 years before. It fits our usage profile very well.
Rusty