I rode from Key Largo to Key West in the middle of May this year. My wife drove the Jeep to where we met and then we stayed in a hotel. The first day we stayed in Marathon and then I biked to Key West.
You can read about my ride at these links:
Key Largo to Marathon FL Bike Ride - Texbiker.net
Marathon to Key West FL Bike Ride - Texbiker.net
I didn't camp but one of the cyclists I rode with on the second day did. He stayed at a campground just as you enter Key West.
Be prepared for bike trails ending unexpectedly.