For Christmas 2011, I rented a car in mainland Florida and drove down to Key West—a favorite vacation of mine. Below is my car-camping guide to the Florida Keys, originally posted on Google Plus, where is it impossible to find.]
THE FLORIDA KEYS - Best cheap winter vacation in America! It's easy: Fly to Miami or FLL (usually cheap), rent a car (cheap on weekends). Stay at the Everglades International Hostel in Florida City or sleep in car. (Since it is warm, the only bedding you need is an airline blanket.) Drive the Overseas Highway to Key West -- America's drive-to Caribbean Island. There's no cheap lodging on the Keys and overnight parking is hard to pull off on Key West itself, but you can get away with it easier on other Keys. (There's a state campground at Bahia Honda, but it's always heavily booked.) Once you figure out how to sleep, there's little cost. Fast food and groceries in Key West and several towns along the way. Perfect bath-water swimming year round. All the environmental ambiance of a Caribbean island at a fraction of the cost. Go now! [Nov. 2011]
My photos: http://Glenn-Campbell.com/album?keywest
UPDATE Christmas 2011: Just visited Key West again for Christmas. Arrived on Christmas Eve and left on Christmas Day. I swam at dawn on Christmas morning on Smather's Beach! On this brief trip, I discovered two new overnight camping spots...
In Key West, you can PARK OVERNIGHT IN THE TRUMAN ANNEX, just outside the entrance for Ft. Zackary Taylor State Park. Map: http://g.co/maps/knb4g - Follow the signs toward the park and you'll see what I mean. There were several RVs parked in this vicinity when I visited, and I spent the night in a rental car unmolested. (Unlike the rest of Key West where they are very rigorous about enforcing no-overnight-parking.) I'm not sure you can get away with tent camping here, but you might. Check out the overgrown area in the far corner, under a pedestrian bridge. Even if you don't spend the night at the Truman Annex, you can park here during the day for free and walk to Duval Street.
About halfway down the keys is another rare overnight parking/camping spot: An ABANDONED MANSION near Layton. Map: http://g.co/maps/ecgn2 - (See my Key West album for photo.) When I visited, the gate was open, with occasional tourists driving in. There are No Trespassing signs around the mansion itself (so faded as to be almost unreadable), but none on the grounds or the gate. Place has obviously been abandoned for years, if not decades. I would have no problem pitching a tent here. (You could sleep in the open, without a tent, except for the likelihood of rain during the night.) You could even sleep inside the building (if you're willing to ignore the almost unreadable No Trespassing signs. (Hard concrete, but you'd be protected from the rain and wouldn't need a tent.) Here is a panorama of the mansion and its grounds: http://photosynth.net/view/d82217c3-3b63-4997-a0a8-79fcc8a2d7cb
A great attraction I discovered on this trip was the dock at Robbie's Marina (Sometimes called Tarpon Landing), where you can feed pelicans and huge fish for a couple of dollars. Another is the Wild Bird Sanctuary in Key Largo (free but $5 donation suggested): Get up close and personal with the pelicans. See photo album: http://Glenn-Campbell.com/album?pelicans
Other Key West notes: The main tourist drag is Duval Street. Walk here at night for lots of entertainment. Stores in town include Publix, Kmart, all the fast food joints and -- most important -- a big Dollar Tree store. Caribbean Swimming at Smathers Beach (bring quarters for the parking meters) or Fort Zackary Taylor ($4.50+ entry fee).