RVing in cold weather

I've posted this on another generic RV board and got mixed replies so I thought a manufacture specific site would be more appropriate. So Here it is:
Being a new RVer, living in the midwest (St. Louis, MO) and heading south for warmer weather, how do I handle the water/freezing issue in the RV? I mean that I am leaving a cold, below freezing at night (20ish degrees) and heading to Florida with a night over in Mississippi/Alabama where it might also get below freezing at night. The system is now winterized. Should I de-winterize it at the first night over where temps might get into the upper 20's, lower 30's and fill with water? Or can I do it at home before leaving where temps should be in the upper 30 to 40's during the day, but still in the upper 20's at night.
thanks

garmp,

We travel to Florida from Michigan every winter, leaving Michigan that day after Christmas.  The first night is always in Kentucky where the temps could go anywhere from 9 degrees to 50 degrees.  We never dewinterize until the second night when we are in Georgia and there is no chance of freezing temperatures.  This year we had to wait until the third night when we made it into Florida.  Temperatures south of Atlanta were still below freezing at night.

We carry water in disposable bottles for the toilet and shower in campgound facilities if needed. 

We have been doing this since 2003 and it works for us.  We have never taken the risk to dewinterize when the temperatures are freezing or below.

It was suggested to me that a PC is constructed with the plumbing within the coach body, including fresh water tank, and by having the interior above freezing, which we would, would prevent the pipes from freezing. But I don't think I want to risk it. A gallon or two of $3.00 antifreeze is much cheaper than any repair cost.
Part 2 of my question:
What do you use as a measuring gauge for the night time (lows) temps? I have a couple of websites/apps I use and try to get predictions, but they are predictions. Latest I have seen was , for the night over, 35. I know if that's cutting it too close or not. Don't think I can rely on OTA TV to get forecasts.
Maybe best to just get up in the morn, check the temp and do the change over then before hitting the road. Just bought a digital indoor/outdoor thermometer for that reason.
Thanks for your input and letting me talk it out.

We use Weather Bug app  https://itunes.apple.com/us/app/weatherbug-radar-forecast/id281940292?mt=8 on our iPhones with pretty good access.  As far as traveling in freezing temps, we try not to; but when we do, we make sure the black and gray tanks have a gallon each of RV antifreeze with antifreeze in the macerator and hose.  as far as the fresh water, in all the years we have lived in an RV, we use the on board fresh water when the RV park water is too cold to use.  As a precaution (depending on temps) we might open under sink cabinets and use tank heaters when available.   

We also use the apps like accuweather has for the smart phones as well as having an indoor/outdoor weather station.  We are generally in an area where we get local TV stations so always check the early morning news.

We also carry a weather radio with us that has the NOAA stations and always set that up for the night.  We just recently purchased a small handheld weather alert radio that you can put in travel mode and it will automatically tune into the NOAA station for the area that we are traveling in.  This was a concern for us because it is hard to know which county you are in when there are approaching storms.  Now the weather radio alerts us as necessary.

On our trip down this December we woke up to 19 degrees in Kentucky. 

We camped for several days in below freezing weather. Our furnace was broken so we were heating with small space heaters. We were not winterized and nothing froze. They weren't great heaters so it was chilly in the living space. It was above freezing but we needed jackets and shoes on. We did have electric hook up. We don't have a heated hose so we didn't hook up to campground water.

We went from warm weather into the cold so our lines had been flushed and sanitized. We kept the holding tank heaters on and opened cabinet doors. We now know that we should have kept the hot water tank on or bypassed and drained it. We don't worry overly much about cold temps. The Phoenix can handle it as long as you have heat inside. I would prep as follows depending on whether you sanitize lines or not:

Rig is winterized, hot water tank is bypassed, water lines are drained or blown out or have pink stuff in them (including the outside shower), there is pink antifreeze in the macerator and dump valves: load at least five or ten gallons of fresh water, turn on tank heaters, keep interior above freezing. Carry bottled water for drinking, coffee and brushing teeth.

Rig is dewinterized: sanitize the lines if needed, put a little pink antifreeze down the toilet and shower and run it through the macerator and dump valves, keep hot water tank on if there is water in it, load water, turn on holding tank heaters, keep interior above freezing using Ford truck heater during the drive then furnace or electric heaters when stopped.

If you are dry camping at a Walmart, truck stop or such, you can run your generator the same as all the big trucks around you do. Make sure you have propane and it is turned on.

Set a reminder on your phone to turn off the holding tank heaters when you hit warm weather.