When cold weather is approaching it's a good idea to turn the heat pads on at least a day in advance, also wind is a lot worse than frost alone.
Your water lines should be fine down to a certain temperature as long as you have your propane furnace running and make sure no warm air can escape from the underbelly, anything exposed will freeze right away though.
Every RV(er) is different.
2013 RAM 3500 Dually Longhorn
2014 Trilogy 3650RL, W/D, Onan 5500, 8000# Axles, IS, 960 Watt Solar, 6x6 Volt Battery Bank, Freedom SW 3012 Inv/Charger