For a lot of us, fulltiming means following the 75° mark whenever we can. And since most are retired when they do this, taking up skiing at our age isn't something we think about doing - though there is no reason you can't do it. To live in the winter in an RV, no matter how well insulated they claim to be, is going to require some preparation to make sure you are comfortable. If you want to do this, make sure that you are looking at rigs with enclosed holding tanks that are warmed by the furnace, or have heating tape on them to ensure that they don't freeze during the winter, ease of filling and maintaining fresh water tank (in really cold weather you want to run of the fresh water tank, filling it during the warmer part of the day), ease of access to your wet bay for dumping during warm part of day, how you can skirt to help block the wind from blowing under your rig, etc.
Barb