You need to define "warm". My idea of "warm" (East Coast FL Native) and my husband's idea of "warm" (MI Native) were radically different.
As a general rule, excluding higher elevations, most places south of I-40 will give you what is considered a "temperate" winter.
As a general rule, the farther from the coast you are (100 miles or more) the cheaper and less in demand campground sites are. This does not apply to high demand waterfront and/or "resort" campgrounds/RV parks.
Every place will, even FL, over the course of a typical or not so typical winter, experience lower than "normal" temps, even down to freezing. Yes, South FL has had freezing temps and it has happened many times in my lifetime (I'm almost 63yo). I even remember it snowing. It didn't lay but it snowed in Ft Pierce. It just had the right conditions. My mother (also a FL Native) remembers it getting so cold in the winter (Jupiter) that the mullet froze to death in the river. The time my black tank valve froze and cracked, I was in Cordele, GA (I-75 Exit 101 which means it was 100 miles from the FL/GA state line) as it had almost a week of unseasonable freezing temps in Jan or Feb. A week later, things had warmed back up to normal. Growing up, I remember the pond in front of my grandmother's house would freeze up at least once most winters. It was often thick enough the hunting dogs could walk across it. I know one of my cousins walked across it too one time (kids!). This was in central FL near Ocala. the "Great Freezes" which wiped out most of the northern orange groves over about 3 winters, reached all the way to the Keys. This was during my grandmother's time (she was also a FL Native). It also took out the big pineapple plantations in the Jensen area. They didn't replant. Most people who live in the area don't even know that Jensen had big pineapple plantations.
So every place gets cold in the winter. It's just how cold is cold. I live in a "plains desert" in SE NM. We had snow flurries today. It was 39F while it was snowing big fat flakes. Too warm to lay and it turned back to sleet then rain. I have been told I moved to the "wrong" desert. But I have watched temps. AZ desert (Phoenix) gets freezing temps about as often as we do. In a few days, it will be warming back up to the 60s. And then it will get nasty for Thanksgiving. Then it will warm back up before it gets nasty for Christmas. And after that, it's really winter.
