Like you I have also considered selling the car as I have nowhere dry to store it. It would be better for the car if it was inside a warm garage all winter.
My car hasn't been too bad, I wash and wax it before winter to give it some protection, after this it only gets the occasional wash until it warms up again.
Now it's got some surface rust in places where the filler that blends the arches to the shell has cracked and a few small patches elsewhere. I'm not too worried at the moment as I'd like to get it re-sprayed within the next couple of years. Underneath was solid when it had the last MOT.
During winter I have more of a problem with water getting in to the car, the windows misting up and a useless heater.