You're welcome!
I don't know a thing about tank heaters, so I can't help you there--I don't know how far below freezing they're effective.**
Most of the things others have talked about are things I don't do--I don't have tank heaters or a fireplace (in my 2002 3670RL fifth wheel), and I've never bothered with using the propane furnace or filling the fresh water tank and using the pump.* (I did find out after owning my Montana for about 3 years that the fresh water tank was full!* I don't know whether I filled it somehow by accident, or if it was already full when I bought my rig used.)* I don't even have a heated hose; I've used the old-school method, described by Rondo, of using heat tape on the water hose.*
My rig does have the "Artic Package" or something like that, which I think just means that there's a layer of Reflectix sandwiched between the floor inside and the coroplast outside. I don't know how much that affects heat loss, or the temperature in the basement.
So my advice on what you should do, in Alabama (and in North Carolina, if you think it's the same weather):
1)* If the campground doesn't make you unhook your water, don't.* Don't fill up your fresh water tank.* Use a heated hose instead.* The purpose of having a heated hose (or a heat tape-wrapped hose) is so you can keep your water hose hooked up to the campground spigot even when it's below freezing outside, and you can just keep using the campground water like normal without the hose freezing.*
2)* Use your tank heaters.* If you're not sure they're going to be enough to keep your tanks from freezing, make sure to empty your tanks before dark every night (or before it freezes).* I think it used to be conventional wisdom that keeping your tanks pretty empty kept them from cracking, even if they froze, because there wouldn't be enough water in them to expand enough to crack the tanks.
3)* For heat inside your*RV--I used the propane furnace in my 5th wheel once for about two minutes, then turned it off and haven't bothered with it since.* I use electric space heaters instead.* You might want to do the same, since you won't have to pay extra for electricity at the campground, but you'll have to buy and deal with propane if you use the furnace.* Open the cabinet doors under the sinks at night, like you'd do in a house, to help keep the pipes warm.
4)* For heat in the basement, where the pipes are, and above the tanks--If you use your furnace, I think heat will circulate down there and keep the basement above freezing.* I haven't used my furnace, but I've used the old-school method of putting a little lamp*down there with an incandescent light bulb that gives off heat--but I don't know that you can even buy real light bulbs anymore.* I've also had a little "personal" ceramic heater down there at times--($10?* $25? at Walmart), which uses only 250 watts but gives off enough heat to make a real difference.* You could also try putting foam pipe coverings on the exposed pipes in*the basement, like you'd do with a house. I've even used Hot Hands hand warmers to help keep pipes warm.
5)* Buy some square foam cushion things to stuff in your skylights, to keep the cold out.* (I can't remember what they're called, but I bought mine at Camping World.)* You could also buy some Reflectix at Home Depot or Lowe's, and cut it so that it fits into your windows.* Don't tape it there, because you'll want the light during the day--so you'll want to take the Reflectix out of the windows during the day--but it helps keep cold out at night.* You could also line your cabinets with Reflectix, as extra insulation.
6)* CATS!!!* YOU'RE GOING TO NEED MORE CATS!!!**
* (Or dogs, whichever you prefer.)
Have fun!