Well then our paths may meet - literally. I'll be there in December as well. Here's praying for blue skies!!
I'm staying at Hosteria Pehoe, in Torres del Paine, between Christmas and New Years, with a few extra days on the front and back ends in Punta Arenas and Puerto Natales. I'm hoping for changing skies, switching back and forth between stormy and partly cloudy. It's hard to get sunrise and sunset color without clouds :-)
As for getting around, I'm renting a car, not an SUV. I was there last February, and while the roads are bumpy gravel, and not all that pleasant, in Torres del Paine they are certainly manageable without 4WD.