How cold is too cold?

When temperatures reach around 32 in the day light hours, it's time. Keep a cup of water, or a pan of water, outside the camper (like near the wheels where it won't get kicked over). Watch it daily. When it starts to freeze and stay frozen, it's time. Here's another method. Put a glass of water in one of your outside storage compartments. There again, when it starts to freeze and stays frozen (you know, begin to get ice on the edges and does not completely thaw)... you know it's time.

It is not just the temperature.

You have to factor in the wind.

I live in the high country in NC at elev 3200 feet, and we get many nights where it is below zero.
My experience is if it is mild during the day and gets down to around 26 during the night, as long as there is no wind, I won't have any problems, but with the same temperature and a 15MPH wind, I can get in trouble, and with that temperature and a 20 or 25 MPH wind, any unprotected pipes will freeze in a heart beat.
I have learned from experience.

We are heading south at the end of November, but I will be winterizing here in about two weeks.

Jack L

Water has a lot of mass, and takes a lot of time to cool down. Just think of the tiny amount of water in the cells of an ice tray in your freezer. It's 0 F in your freezer and it still takes hours to make ice.

Not sure where you're at, but in Michigan we're dipping below freezing for maybe an hour or two just before sunrise. That's not enough time to freeze water inside pipes, let alone holding tanks.

Best advice I would have for you, if you're in / near a farming community, the government will issue FROST and FREEZE advisories and warnings. If you get a freeze warning, that means extended times below freezing is likely, and you may want to take action to protect your plumbing.

In other words, it's not really how cold, but how long. A few hours before sunrise, no problem. If it's in the 30s when you go to bed at 11pm and expected to bottom out in the 20s by sunrise, then you might want to worry.