it's kinda silly to leave it running though. because both will cycle on and off. so either you run the genny every now and then to let the frige and freezer turn on (and guess when it needs to be run) or run it all the time, but sometimes under no load.
a better way to go would be a charger
. let the freezer and fridge run off the inverter
. and run the genny to charge the batteries when needed. as it's easier to know when the batteries need charging
vrs when the fridge or freezer need to run