We fulltime in our 2011 rushmore here in panhandle of texas. Winters (last two) haven't been kind. Get a good heated water hose. I put foam pipe inslulation around mine and run the hose under the trailer and then skirted w/ cedar fencing and rigid foam insulation on north, east and west sides. Skirted south side with 4 x 8 siding cut to fit. built it in sections and when in place put one cedar siding board upright to tie the sections together. I only need to remove about 2 dozen screws and the skirting is ready to remove and stack for travel. It is relatively easy and cheap to cut the rigid foam insulation to fit the bottom of your living area slides and gorilla tape or block up to undersides of slides and does help a great deal. Also have used the foam pipe/hose insulation as fillers in interior area around slides. When wind gusts hit 35-50 mph there is an ovious amount of air infiltration around the slide gaskets. I don't have the name of the item, but some of your feed store/ag type places or ebay sell a thermo-cube. is turns one plugin outlet into 2 or three and has a thermostat in it. Plug one into your basement plug and then run a droplamp or small electric heater from it. I believe the thermostat comes on at 45 degrees. It is essential you use your propane furnace as some heat is directed into the underbelly when it is running. We have had the fresh water drain freeze on us and it blocked us from getting anything from our freshwater tank, but will remedy that situation this summer. The heated hose we bought was a Privit brand i believe. Real heavy duty farm/livestock hose ok for potable.
As far as sewage, I have left mine open, but have my hose enclosed in a 4 inch PVC pipe at a pretty severe angle down, so have no low spots for sewage buildup. Have not had any problems with it. I do not leave gray tanks open, but dump when full. Be careful leaving a faucet dripping, as if drain hose does freeze up, sink etc may run over.