I disagree that you need to commit for the entire peak season. We don't leave snow country until late November or early December returning home in mid March. This year we stayed in Tucson for a couple of days. We rented a space in Tucson for December. The resort has 1200 spaces with probably 100 empty sites left. We are spending January in Apache Junction which required making reservations in July. February we're in Wickenburg, Arizona which required reservations in months in advance.
Over the last five years we have seen more vacancies even at peak times. This includes the big CalAm resorts. You may be limited to a few days or weeks rather than a month. You probably don't want to spend the entire season in one place the first year. We are on our sixth snowbird season and haven't committed to longer than a month in one place yet even though we do return to some places every year.