Oddly the year of the Rv can make a difference. For a long time, wire manufacturers used corn-based plastics for shielding on wires and they attract rodents. Many still do. So, it may be less about food and more about wires and insulation for housing. I would discourage poisons as they can let rodents die inside the walls which trades one problem for another. Plug any holes in the RV with steel wool. This can be a daunting task because once you start examining under the rv and under cabinets, in bins etc, you'll find a lot more holes than you thought. If the RV is not plugged in the easiest access would be tires to climb into the RV. Some deterrents around the tires would be a start.