We go to Florida to escape the snow. This will be our 4th time south and each trip has gotten longer, leaving earlier. It went from about 6 weeks, to 9 weeks to 3 months, to this year leaving late November until late March. People we have met in FL told us they pretty much did the same thing, longer each year.
First year and part of the 2nd we hop scotched around FL, staying in different RV parks to get the feel of the part of FL that we preferred. We stayed in one park 3 months last year and will do 4 months the same place this coming year. Also, the rates are less expensive north of the Tampa/Orlando line and the further inland the less cost.
We have friends that do Gulf Shores, AL and the temps are quite chilly in January/February. They also do it in a condo rather than an RV. I think the gulf coast north of FL is too chilly. We've traveled to South TX once, but not sure we want the windy/sandy experience for a length of time. We're north of Tampa about 75 miles and it can get close to freezing about 4-7 nights per winter, but the days usually warm to mid-60s by noon. Late February and March are usually nice and warm.