How far south?

People are recommending Kentucky and Virginia, but my daughter in Nashville was buried in snow (snow emergency shut downs) before the end of December at least twice in the past five years, and last time I went through Virginia between Christmas and New Year's I was driving through snow. My last trip through Kentucky, it was snowing from Bowling Green through Louisville to Cincinnati, and I got stopped by ice covered roads just north of there.

To be relatively sure to avoid snow (and the ice storms more common across the middle South) late December and into January, I would stop somewhere south of Interstate 20. Make that Interstate 10 if west of the Mississippi, because north Texas can also get buried in snow well south of Dallas-Fort Worth, as I've been caught in a Christmas snow storm in northern Texas twice in the past 12 years.

On the other hand, I've made many Christmas trips to southeastern and south central Michigan in the past 33 years, encountering no snow anywhere along the way. But that's variable, and not predictable over much more than a week. Other trips through that area I've been shut in for a day or two by winter storms across Missouri and Illinois, and across Tennessee, Arkansas, Georgia, Alabama, and Mississippi on Christmas trips to North Carolina.

Even Kalamazoo may not be snowy at the end of the year, but I would not count on that because of the lake effect snow reaching that far.

Orlando

We have been in an ice storm and stuck for 3 days in Austin TX. ElPaso TX usually gets snow once every other year. 2 years ago, while in Carlsbad NM we sat out in our shorts and the next day it was 20 degrees out with snow that night.
It's called "watch the weather". But really usually south of the Missouri border is okay.

I would keep an eye the 10-day forecast on Weather.com for temperature trends leading up to your planned visit. I live very close to WMU and weather here can vary greatly at that time of the year. It could be in the teens or it could be above 40 for an extended period.

I'd say that you'd be fairly safe in the Louisville, KY area or a bit south.

What is your final destination?

We usually dewinterize at Cave City, Ky. That is our second night out and it has worked for the past several years.

LOTS of folks would starve to death if they had to predict the weather for next December ANYWHERE in the country :) For what it's worth, in just the last couple of years Oklahoma has gotten quite a bit of snow so it's looking like somewhere in Texas would PROBABLY be safe.

X2 on Kentucky but even they can get cold and snow.

Depends where you're going.

I usually dewinterize at Memphis but I've seen low 20s even into northeastern Texas.

If your route south is along the I-77 corridore, Camp Creek SP in WV is open year 'round, 19 sites with electric, 7 with W/E. Depending on weather, water can be an issue. You'll find FHUs at Ft. Chiswell RV Park in S.W. VA and as you travel I-77 south into the Carolinas, you'll find more and more opportunities on down to Florida.