I am having the same problem on my 2001 Holiday Rambler. I have tried to find the isolator but the large guage wire from the battery post on the alternator disappears into a mass of plastic wire loom and I have yet to be able to locate the isolator.  The inverter is pulling about 36 amps with the refrigerator running but the alternator is only showing about 12 to 14 amps at 14 volts with the engine at idle so I don't think the house batteries are  getting charged.  I checked the voltage on the D