I'm a rookie so take this for what it's worth.
Are you thinking of moving around or sitting in one spot for the winter? We move around, at least for the 2 years we've been heading south. Our small 21' fifth wheel works fine for the 2 of us, moving around every week or 2, for 3 months. If we were to sit in one spot we'd want something a good deal bigger. You need to decide if the size trailer you can pull with your truck for 1500 miles is big enough to live in for however long you want to go south.
Costs us roughly $200 a week to stay mostly in state parks, add in gas, food, general spending and it's about $700 a week, for us. You can get better rates if you stay in commercial campgrounds and pay by the month or the season. Prices for camping vary considerably, $300 or so a month and up.
We spent some time this year in MS, LA, AL, and northern TX in Jan/Feb, cool but not bad. The cooler it is the more time we spend inside. We'd need a bigger camper if we wanted to spend more time in these areas.