Towing - Stay in RWD or change to 4WD?

We just purchased our first camper this past Monday and we are making our maiden voyage tomorrow. Our tow vehicle is a 2013 Expedition EL and it has an option for 2WD, 4WD Auto, 4WD High, or 4WD low. Since I am new to towing what would be the best option to tow in?

Thanks