For a cold snap of such a short period you really don't need to do too much. If you can keep the furnace running (set to 55-60 over night) it will blow warm air into the wet bay and keep it above 32 degrees. FILL the fresh water tank as it will absorb heat during the day/evening when you have the furnace running and return that heat to the cooling areas at night. You won't need anti-freeze and you won't need to stop using any of the facilities. Just be sure you don't run out of propane! Assuming you have an electrical plug in the wet bay somewhere you can plug in a worklight with a "real" bulb and the heat will help keep things warm. They also sell "personal heaters" that put out about 250 watts. Leave one of these in the wet bay with access to the tanks and plumbing and everything will remain toasty warm.
THIS ALL ASSUMES that your dump lines and pipes are all internal to your coach. If you have any plumbing hanging under the coach then you will want to wrap that with insulation to prevent water in the pipe from freezing. Where is the dump valve located? Inside a heated bay? If so, the outside pipes are of no concern as it/they will be empty.
We have camped in negative # degrees many times for extended periods without issue but all of our plumbing is internal and stays toasty warm. We also put a remote temperature probe in the bay to ensure we are always aware of the temps down there.
Our job has taken us to Minot, ND this year and we are there now. HOWEVER, we chose to drive the car and stay in the company condo as it was -21 this morning and it will have been 2 weeks since they have seen a temperature above 0! "A man has got to know his limitations" (or something like that).