We have a single slideout that we pull in for really cold weather with a roller awning to keep the snow off the top of the slideout . Having a lot of wet ski gear and clothing will make you appreciate the extra room. If you are boondocking at a ski resort without electric hook up, you will be relying on your propane furnace to keep you and your basement water tanks warm. Solar will keep your lights on, refrigerator and furnace fan running, maybe run your heated tanks. A generator will help for cloudy days, but not for long term boondocking. You should also get thermal windows.
But I think a Wave Catalytic heater is what you want if you want to stay really warm. With little fans to blow warm air into your basement so you don't have to run your furnace all day and night (have to keep it warm during the day so your pipes and tanks don't freeze). Search some conversations here about Wave heaters.
Long term cold weather campers have a larger external propane tank that they get a service to fill on site so they are not pulling out the 30 pound tanks every few days.
We keep our skis in a rocket box on top that we access from a 8 foot step ladder we also use to clean snow of the roof. If we stay at a campground near a ski resort we leave the pink antifreeze in the water lines and use the campground rest rooms and not worry about the Basement temperatures. Also if you get a diesel you want to think about an engine heater when it is time to leave.
