If you have full hookups and don't want your hose to freeze, you can drip the faucet. I've been out many times below freezing. Even if I have full hookups, I will fill the fresh water tank in the trailer (at least partially) just in case the supply hose freezes. That way you will still have water. Also, make sure your propane bottles are topped up. I have an electric fireplace that puts out pretty good heat, but the furnace still kicks on occasionally. My prior trailers didn't have any electric heat and a long weekend below freezing will run the inefficient RV furnaces pretty hard. I know many that Winter camp have small electric heaters so they can save propane.
Other than that, it should be just like camping in the Summer.
j