We've been Florida residents for 43 years and don't think humidity is much of a concern during the November-March time frame, but I would still suggest some ventilation at the very least. If you don't mind the electricity cost, leaving the a/c on is fine. There will be plenty of 80+ days where the a/c runs and, if the RV is parked in the sun, it will heat up inside to 80+ much of the day.
A dehumidifier is a good solution if you have a way to drain it, e.g. the RV is hooked to a sewer so the gray drain can be left open. However, it should be sufficient to leave a ceiling vent fan on and a window or two open a crack, so that fresh air can move thru. Our coach always sat in our yard during fall & winter and we never ran the a/c - just kept some windows open.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC