A lot depends on how your RV is constructed with regards to cold weather operation.
Many (but certainly not all) RVs have the piping and tanks enclosed within the heated envelope of the RV, so the plumbing system can be fully used in freezing weather so long as the furnace is used (and the water heater at least occasionally fired up). You do have to use water from the fresh water tank rather than leaving a hose hooked up to the campground water supply (connecting only to fill the tank and disconnecting and draining out the hose afterwards).
If the RV is not set up for cold weather use, and has exposed piping and holding tanks and so forth, it's a lot harder to use the plumbing system. Some put rock salt in the holding tanks (to prevent freezing) and flush with water from jugs etc.; some flush with RV antifreeze and don't use the sinks.
In very cold weather, the fridge may have trouble; some put a light bulb or other heat source in the outside fridge compartment to keep it somewhat warm, or cover some of the lower vent cover's holes with insulation of some sort to help keep the compartment warmer. Searches here will turn up good information on the problem. For a short trip, it may be just as easy to use a cooler and put snow or ice in it to keep it cold.