How cold does it have to be to winterize the RV?

It is how may hours at 31 can't you go.

If you get under 20 at night, or above that but without being above freezing during the day, or just barely, you are risking getting things broken up. Outside showers are one of the worst, followed by exposed pipes and drain valves, and after that... almost any part at all.

But if you have a modern C with it's drain pipes all enclosed, and some ducting to all cabinets that have water lines in them, put your furnace on at 50 and keep your propane up so it stays warm.

If it's an older unit, don't risk breaking it for want of a little smelly pink in the lines, learn on here how to do it right and then clean it out when you are into a safe place.

Above all, study all the methods here, there are so many places people forget to winterize, and if this is your first one, it's a big learning curve and you might as well go for it now and keep on reading. Lots of pitfalls and traps along the way will give you anxious moments.

Usually takes extended periods of hard freezing for pipes to freeze, so if you're getting into the high 40's or above during the day you're *probably* ok. To be safe, you could drain the water heater and open low point drains. I would probably just run heat on lowest setting and open cabinet doors. This assumes you have no exposed water lines. Just my $.02. Have a great trip.

A month is a long time with the weather turning. I'd drain the water heater and put a gallon and a half of rv antifreeze through the water lines. I winterized mine today took maybe 15 minutes with me pumping the antifreeze and my wife talking to me on the phone opening each faucet till the pink comes through. I use a hand pump bought from Campingworld.

Water freezes at 32 degrees. While a few degrees below that for just an hour or two probably will not be enough to freeze solid any water in the pipes, anything more than that is a risk. Only you can judge how much risk you are willing to take.

If you are going south and your overnight temps are that much below freezing, be safe and leave your furnace on 50-55.
Are your holding tanks heated??
Also, be careful with the hot water tank as it is insulated to the inside of the coach and the furnace won't help. You would have to leave the hot water tank on also to be safe.