These cars have already lasted for 50 years. I tend to over-think things, so if you're like me, go easy and don't worry too much about it. but I just finished my third cup of coffee, so brace yourself for some overthinking.
I can think of some things you may want to consider, when storing your vehicle in a cold climate for 6 months or more:
1. battery. heat is the bigger enemy to the storage life of a battery than cold. lead acid and AGM batteries lose some charge just sitting. something like 5% a month. more, if you keep the battery connected to the electrical system, because there may be a clock and/or other items in there drawing current 24/7. a battery tender is one way to keep the battery happy and charged, but be careful, some of the cheaper ones are constantly charging, and this can cause sulfation and diminish the charging capacity of the battery over time. But there are some nice battery chargers/tenders that resolve this issue, like the NOCO Genius battery charger, where you can keep it connected for years, and it keeps the battery in top condition.
2. fuel. store with a full tank. the ethanol they put in petrol doesn't store that well. but its not an issue for many cars. if you're worried about it, include an additive at your last fill-up before storing. I like using STA-BIL 360 for this purpose. As a general rule, aircraft are often refueled immediately AFTER a flight and parked, so the tanks are full, and there is little empty air space within them to minimize the accumulation of moisture, which can taint the fuel and rust the storage tanks. The fuel in the float bowls of the carburetor can go bad without an additive, maybe even with. if you're really concerned about fuel causing damage, you can run the carburetors dry of fuel by blocking the fuel from the fuel pump while the engine is running.
3. tires. the tires can go flat and even (common storing motorcycle) develop flat spots. if you're storing for extended periods, you can put blocks of wood or jack stands under the frame rails to keep the weight off the tires. keeping them away from the UV rays of the sun is another issue, but not when the car is stored in a deep, dank, dark cave, garage or shop.
4. moisture. this one has bit me in the past. when temperatures fluctuate between day and night, the moisture in the air condenses on the glass and interior and can cause mold, mildew and rotting. there are a few ways to address this. a car port in parts of the planet with big swings in temperature are the biggest enemy. an uninsulated garage is better than a carport. better still, a residential garage with a water heater, where the heater operates a few items a day does a great job keeping things dry. when "stored inside" keep the windows cracked allowing that air drying cycle to keep things nice. without this, you may need a tiny (and gentle) heat source to keep things dry in the interior.
5. paint. If the area where the car is stored will have traffic, like squeezing by the car to get the mail, each day, I favor NOT covering it. when a car is covered, and kids and people are walking by it, they tend to think its protected, and become a little careless by rubbing against it, leaning their bikes on it, placing items on the hood, etc. when the car is left uncovered, I find people are much more careful around it. but in an area that won't see much traffic, I favor a cover to keep the dust off the paint, just make sure the interior can still see some ventilation, if the moisture things seems an issue.
