Florida Campgrounds

The only RV Park on Pine Island that amounts to anything at all is a KOA and $$$$

I would suggest Pine Island down near Fort Myers. This Island is laid back and a lot of fun. RV park has a great pool, plenty of bars and restaurants near by. Check it out.

http://www.rvonthego.com/florida/pine-island-rv-resort/

http://www.saintjamescity.org/index.html

http://www.bertsbar.us/

Toss up on temps in winter in Florida. You are not going to find much availability that far south and some limited availability up in the north. I have worn shorts in North Florida on Christmas day and seen freezing rain once.

As to weather, well it's possible to be cold, (freezing) no matter how far south you go. Consult with farmers almanac and the Weather with Andrew, which is a world wide analysis of probable temperatures due to major influences like El Nino, Artic fronts, (which move south), and pressure centers at the surface. As to any places having open sites, that's about 5% so if they are booked ask to be put on cancel last minute list. I think the weather is predicted to be mild, and not freezing, but that could change.

Sugar Sand RV Resort, Matlacha, FL
This is exactly what you are looking for.