What condition is the car? Driver?
I would just give it a nice coat of wax and leave it outside with NO cover. Covers used outside are uaually not good for a car, lets moisture build up, and if its windy, the cover/tarp will scratch your paint. If you have nice wheels/tires cover them or put on another set.
Interior, put alot of laundry dryer sheets in the interior and trunk, it keeps the mice out and works great, plus your car will smell nice come spring time. Make sure your floor vents and defrost vents are closed and flip your sunvisors straight down (mice like to nest here if you don't), also if you have the shoulder belts that clip to the roof let them hang down too. If you have alot of mice you can put some sticky traps inside the car but check them often so if you get one you can get rid of it. Also vacuum the car out good so it is clean.
Keep the sun out...use a sun-shade for the dash or I just cut cardboard to fit, also use a cover on the rear seat/package tray, even the sides too.
You live north east? They get lots of heavy snow, a portable garage/shelter may colapse on your car, you will need to clean the snow off regulary. I have always wanted to use one of these shelters but am afraid it will blow away, besure to anchor it down good. If you do use a shelter, I would still do the things I mentioned earlier.
