What can we do to help preserve our vehicles when they are out of use? Here are some ideas, although I'm sure I've left some things out. Different parts of the world take different precautions. Let me know what I've missed.
Engine
Run your vehicle at least an hour, under load, to drive water vapors out. Don't start and run it for a few minutes this does more harm than good. Shell Oil has a special storage oil for aircraft that you can change to, then run, then store. This is a preservative oil.
Special fuel additives, or stabilizers, can be used. You can drain all the fuel from the vehicle. Or you can use aviation gas (avgas) for the last tankful. Avgas doesn't go bad, it just eventually disappears. Some of your money disappears as well; in our town avgas is about $2/gallon.
Early engines (1937 & earlier, I think) with 18 mm plugs can use dessicant plugs designed for aircraft.
You might want to turn the engine over, without starting, to "park" the pistons and rings in a new spot and have different valve springs compressed from time to time.
Drain the cooling system, or use antifreeze to protect it to a colder temperature specification than you expect to get where it will be stored. If you freeze the antifreeze/coolant in your block, you've lost the engine. If you freeze and crack your block when it's full of your best antifreeze solution, you need to move to a warmer climate.
There are various aerosol products, from light oils to Cosmoline (this comes from Missouri), that you may spray on the engine and accessories. Remember to protect brushes and commutators in the generator and starter by taping up the air holes before you spray. You will need to remove most of the heavier products in the Spring. The better they are at protecting, the more difficult they are to get off. Cosmoline can be removed with a 50/50 mixture of solvent and elbow grease.
You can unbolt the fuel pump stand to allow the fuel pump spring and diaphragm to relax a bit.
Tape plastic over the air cleaner and crankcase vents you can also include a permeable dessicant pack inside the plastic.
Battery
Disconnect the battery from the vehicle and keep it at full charge. If possible, move the battery to a warmer location. This avoids freezing and destroying the battery. A warm battery can produce more cranking power than a cold one.
Windshield Washer
Drain the washer, or use nonfreezing windshield washing solution.
Tires
This applies especially to bias ply tires. Store the vehicle on blocks or jack stands to avoid flatsiding the tires. If you put the blocks or jackstands under the frame, this also take much of the stress off of the axle springs. At the very least, keep the tires fully inflated.
If your storage area has the potential to house critters like insects or rodents, deny them access. I have seen jack stands in pans of turpentine. Another possibility is mothballs in the interior. Don't let your Ford seat cushion become a comfortable "mouse house."
Brakes
If you are using nonsilicone brake fluid, consider wrapping a baggy around the master cylinder to limit the uptake of moisture.
Don't leave the emergency brake on the linings could rust to the drums.
Clutch
The organic disc linings can attract moisture and rust to the flywheel and pressure plate. Sometimes that requires a teardown to fix. Some people block the clutch pedal in the disengaged position to avoid this. The pressure plate springs would then be stored more compressed, which could accelerate their failure. I would suggest that you, at minimum cycle the clutch pedal once a month.
Interior/Soft Goods
You may want to leave a light bulb on in the vehicle as a small heat source. Be sure to block it so that it cannot touch anything flammable or anything that could be damaged by prolonged exposure to heat. Golden Rod makes a low wattage heater for this that is safer in areas of high humidity. Even a small elevation of temperature drives away damaging moisture.
Exterior/Paint
There are many types of covers available for protection - both indoor and outdoor.. There are zip-up bags, some with their own climate control, some with dessicant paks. Don't put plastic film or tarps directly on the finish to avoid damage.
A Penny Saved....
If your vehicle will be out of service for awhile, perhaps you can save some money by changing insurance coverage and/or registration to "nonoperating" for the period of nonuse.
That's all of the ideas for now. I would like to hear from other members if they have other storage practices that work for them. Many thanks to Joe Raab and Henry Williams from the (This email address is being protected from spambots. You need JavaScript enabled to view it.) group for input on this topic.