We have a 2012 390BH-60 with a large side-by-side Dometic Frig. Without running the frig in inverter persay ... in propane, one the frig is at temp, I am able to get the better part of a week out of the batteries. Be careful of other phanton draws ... the convection microwave display in particular.
We used out MH almost constantly between spring break and the start of Sept ... bringing it home for only a week or so at a time. When we had the unit at home, we left it loaded both with clothing and food. It would sit on the driveway with no access to 220V power. Unfortunately the parking orientation meant that the unit face westerly in the afternoon ... thereby taking a lot of sun to the frig side of the unit. By openning the awning and unplugging the microwave, I was normally able to get about a week before I would need to run the genset.
Someone please correct me if I am wrong ... but my understanding is that by turning on the inverter, you are allowing the frig to change the ccoling function from propane to electric and thereby dramatically increasing the draw on the batteries. If you leave the inverter off, the cooling is done by burning propane and the only electrical draw by the fric is to run the control board.