The best way to store any car for the winter is to do the following:
1. Change the oil just prior to storage. Oil absorbs moisture (a natural byproduct of combustion) and if old oil is left in the motor, moisture will evaporate out of the oil and condense on the engine internals causing corrosion. Also, oil becomes acidic with use and should be changed for this reason also.
Change oil, start engine and run just long enough for the oil to circulate, then shut off for the season to prevent a buildup of moisture. If planning to change the tranny fluid in the coming season, it's also a good idea to do this now for basically the same reason.
2. Loosen the spark plugs and shoot either fogger oil or a squirt of motor oil from a can into the sparkplug holes - about 1 tsp. This will prevent the rings from corroding and seizing to the cylinder walls over the winter. Upon initial startup in spring, oil will burn off in the 1st few minutes.
3. Increase tire pressures to 40PSI. This will prevent flatspotting and leaks. The tire pressure will drop with ambient temp. Some will say to put the car on blocks, but with modern independent suspension, it's not good to leave it 'unsprung' for long periods.
If you want to get really anal, fill the tires with Nitrogen. This is a Dry Gas and will prevent Dry Rot. Nitrogen can be obtained from any welding supply.
4. Store desiccants in the car. These can be purchased and laid on the floor front/back. This prevents mildew from growing and keeps leather from deteriorating due to accumulated moisture.
Also, the 'Car Cacoons' currently being sold are very good for long term storage and use only a couple bucks electricity the entire season, also reduces door dings and the like. Absent this, use a quality car Cover.
5. Wash the car - don't allow pollution, Tree Sap etc. to work on the paint through the winter.
6. Remove battery from the car and put on a maintainer, preferably inside where it's warm. Be sure to allow plenty of ventilation to prevent Hydrogen Gas buildup.
7. Place the car on a sheet of Vinyl laid out on the garage floor. Make sure the vinyl extends 2 feet from any edge of the car. Garage floors seep moisture through the winter which can condense on the underside of the car, suspension, etc. causing corrosion.
8. Fill Gas Tank with Fresh, Premium fuel. A partial tank will corrode from moist air. Plus, it'll probably be cheaper than filling it next season.
9 Check Anti-freeze to be sure sufficient for temps anticipated - not relevent to an A/C Flat 6. http://mercedesdoc.com