What are all the procedures one should follow when storing a 2000 Audi tt outside for an entire northern New England winter?
a good car cover and a bottle of fuel stabalizer or heet
I would try to find inside storage. In any case there are a few things to consider:
If you use a cover on it, make sure it is a very good cover. A few months of wind blowing that cover over the same spot can wear through the paint.
Cars can become targets for critters. Various rodents and others can make a home in your car doing a great deal of damage.
I recommend removing the battery (after making sure I know any security codes that might be needed in the spring. Take the battery inside and put a battery tender/maintainer (special battery charger) to keep it charged and to make it more difficult for anyone who would try to steal it.
Cancel your collision insurance as you will not be the cause of any accidents when parked, but keep the comprehensive active. See you agent for details. You can save a lot this way.