We too travel south once Christmas is past us and we've had a month or so of skiing.
The hydraulic slides work fine in the cold (hydraulic landing gear and jacks too), they just run slower.
What we do is heat the trailer up a couple of days before we go, get the fridge going, and load 'er up.
The first night we stop where the temps are usually still below freezing. Last year they also had about 3' of snow on the ground so had to plow out a site each time someone came in.
For that night's stop we stay hooked up, we don't put down the landing gear, we put out the slides, crank the furnace and a couple of ceramic heaters. Then, because the next night's stop will be significantly warmer, we'll de-winterize as the underbelly stays warm enough overnight with the furnace running, as does the basement and the universal docking station. For water, we'll \put enough water in the fresh tank to do us for that night.
For us the biggest issue is the weather. We try to give ourselves a wide window so we can adjust our departure date as needed, based on the forecast. We had to delay a day last year, in fact. And even then, though the forecast was good, we had about five hours of towing on heavily snow covered roads.
