Google "storing classic cars" and you'll get a large number of hits. They all pretty much say something like this:
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10 Tips for Long-Term Classic Car Storage
Make sure your gas tank is full. This will reduce the amount of water that can be absorbed by the gasoline and it also slows the rate at which it turns to varnish. Use and additive like "Sta-Bil", "Dry Gas" or similar. Make sure it's well mixed and run the car for a while to make sure it's in the entire fuel system.
Freezing temperatures naturally dictate that anti-freeze be used. But even if it's not freezing, put it in. Many of the newer 'coolants' have excellent corrosion inhibitors that will help protect and lubricate your cooling system. A 50/50 anti-freeze/water mix is fine. Again make sure to run the car so it's mixed throughout the entire system.
Change the engine oil. Dirty oil is contaminated with acids and water that can cause premature bearing failure and rust inside the engine. If the car is likely to be left for a very long period of time unattended, remove the sparkplugs and liberally squirt some form of 'upper-cylinder lubricant' into the cylinders before replacing the plugs. This will help stop the piston rings from rusting to the cylinder walls.
Make sure the Brake and Clutch master cylinders are full of brake fluid. Brake fluid can absorb water very quickly. By reducing the exposed surface area of the fluid, the water absorption can be reduced. If you can, bleed the brake and clutch systems. It is recommended that you do this on an annual basis anyway, to purge the system of old and possibly contaminated brake fluid.
To inhibit rust in the engine area, use a lubricant spray such as WD40 to coat all exposed metal surfaces. The volatile carrier in the WD40 will soon evaporate leaving a protective film on the hose clamps, coils, carb bodies etc. 'Wax-oyl' is also good, but you'll want to hose it off at a 'car wash' in the Spring.
Wash the entire car and apply a good wax. Don't forget to clean the inside. Do this early in the day to give it plenty of time to thoroughly dry before putting it in storage.
If you have a convertible top, leave it up and the windows and vents closed. A convertible top can develop nasty creases when folded for long periods, especially in cold climates. Treat Vinyl tops with Silicone or similar. Keeping the windows and vents closed keeps small creatures from entering. But buy some desiccant sacs from a storage supply house 'Dry Pac' for example and place them inside the car on the floors. This will keep moisture from damaging the interior if it is damp or humid where you are.
Ensure that the boot is clean and dry, The boot seal is not always positive and some moisture can collect and condense in the inner fenders and floor. Air it out well for a day or so, then place a desiccant sac in here too before closing it up.
Finally, take the car on a good 30 minute run. This will evaporate all the moisture in the exhaust and in the engine. Then park the car with the hand brake off and either 'chock' the wheels or leave it in gear if necessary. Over inflating the tires can help guard against flat spots. Disconnect the battery.
The best thing to do for a stored car is to visit it once a month and take it for a short drive. This keeps everything in good shape, preventing things from getting corroded and seals drying out. At the very least have some one start it up periodically. If you are going to cover it use a proper Cloth car cover, not a Plastic one. If you find the concrete floor in your storage unit gets damp or 'sweats' use cat litter, or lay plastic beneath the car to prevent the condensation from reaching your floor pans. "
Also, check this out
http://www.carcapsule.com/. It is much better than a regular car cover in a number of ways. First, there's a small fan which supplies a constant supply of fresh dry air. It will protect your car from inadvertent impacts, and lastly you can see and enjoy the car all winter. I keep meaning to get some of these. Maybe Santa will bring me one.