We have a 2013 ERA and the battery cutoff switch is just under the counter. It is a small rocker type switch which obviously only trips a relay. It does not carry all the battery power. Our ERA 70A might be a bit different than yours, but the manual we got describes the switch in detail and says where it is. Yours will likely as well.
As others have said, running the genny to charge batteries and then use an inverter is not cost effective especially with a LP genny. Just run the genny when 110 volt is needed for a short time. Far more efficient.