Make a few overnight trips in the RV without water in the tanks. If you don't put any liquids in the fresh water tank, or the holding tanks, you can use the rest of the RV as often as you wish in cold weather. You won't be able to test for leaks, test the water pump, etc. But, you can check out a good bit of the other systems. You can test your furnace, generator, batteries, slide, levelers if you have them, refrigerator, all of the electrical outlets, the microwave, cooktop, TV, all of the lights, etc.
If you have a couple of plastic tubs for the sink, you can wash your hands by having someone pour water out of a bottle over them. Then, empty the water in a tub into a jug using a funnel. Use the second tub to catch any spillage so that it does not end up in the sink.
If you line the toilet with a 30 gallon trash bag and put some kitty litter in it, you can do your business there, then put a little more kitty litter over it. It works for cats. During our tent camping days, it worked for us. We had a travel toilet that amounted to a seat on a frame that had a trash bag suspended under the seat. Amazon sells them. If you use enough kitty litter, dispose of the trash bag daily and reline the toilet, there won't be an odor problem. At least that is our experience.
