With a modern vehicle the charge voltage will be at least 13.5 volts, probably more. That will charge the house batteries 100%, though it may take a long time, and only if the charge wire to the camper is large enough to service the house loads. If you have your refer on DC for example, it is drawing around 30 amps. The #10 typical of a 7 pin harness will be dropping about 1.8V in the 60' round trip on the wire. Now your 13.5V is only 11.7 and, yeah, no charge, in fact it will drain the house. May burn up the 7 pin too. Change that wire out to #6 with a proper connector, and even at the same length and amperage, you will have a 0.7V drop, your 13.5 volts is now 12.8, almost no charge but at least not draining the house battery
A DC to DC charger placed near the alternator, without remote sense, does not solve this wiring problem, voltage will still be low. Placed near the load, or with remote sense near the load, it band-aids the problem: It will boost the voltage back to where is it supposed to be, at the cost of drawing even more current through the inadequate wires.
You need to address the wiring problem first, then consider a DC to DC charger. Or don't run large house loads (like the refer) on DC.