Depends on your expectations.
If you want to be warm most of the time, then South Florida is the place. It is full of RVers who go down there to stay for the winter, but short term stays are still possible if you search.
If you don't mind southern winter temperatures and are just concerned about freezing, staying close to the Atlantic or Gulf Coasts works for most of the winter. On the Atlantic coast, you want to be within the influence of the Gulf Stream, which means mostly south of Cape Hatteras, although long freezes have been rare as far north as Hampton Roads (which does average a few inches of snow per year). But it can also get cold much more to the south, as I've experienced sub-freezing nights trying to tent camp at Daytona in early February.
Generally, more likely to be warmer the more you go to the south, and when it does get colder, more likely to be sub-freezing the further inland.
One of my cousins goes to Fort Myers for the winter, it gives him the most riding days, and from there he more often rids south, to Naples or across the Everglades to Miami or the Keys. But when it is warmer, he rides north.
Another cousin winters in Hernando County, which is sometimes warm, sometimes cold, but most of the time mild.
My brother lives in Citrus County, which can get below freezing, but is usually mild, not so often shirtsleeve warm.
My sister makes late winter trips to the Outer Banks, because coming from Michigan, being on the beach, above freezing, with no snow, is good enough for her.
Tom Test
Itasca Spirit 29B