In freezing weather, you'll either need to disconnect the water line or use a good quality heat tape. You should cover the roof vents from inside with foam inserts (mine are made by Camco). Also, open the cabinet doors under the kitchen and bath sinks when it gets in the 20's or lower. When it gets below 20 degrees, you should add RV antifreeze to the black and gray tanks. RV's have a large window area compared to a sticks and bricks house. So, it's a good idea to cover the windows with plastic in the winter. Also, expect to use an obscene amount of propane for heating. However, if you have an electric hookup, electric space heaters will help.
I live full time in my travel trailer. However, the areas where I camp in the winter usually are not that cold in the winter. Sometimes in the teens. So, I'm very comfortable in my TT. I hope this helps.