How To Store Vintage Port
Most modern residential property is unlikely to have a deep and dry cellar, with the right level of humidity, so it's not unusual for wines to be stored in the cupboard under the stairs, or with a local wine merchant. Fine wines including Vintage Port prefer a stable, dark environment with a temperature between 11 and 15 degrees centigrade. It's not so much the temperature but rather the variation within it that is the problem. If the wine will be stored at home, it's essential for it to be far away from windows and radiators.
The bottles should also be lying down, and preferably not moved. Sometimes bottles will have a white paint mark on the bottle. This is to identify which way should be up - the white mark should always be facing upwards. This allows the crust on the wine to develop uniformly in one place; another reason why the bottle should not be moved.
Wine merchants sometimes offer a storage service if you are buying a case; sometimes even for a bottle. It's worth asking.
For very old bottles of Vintage Port (1963 or earlier), the cork should be inspected for seepage once a year. Quality wine merchants may offer a re-corking service to give the bottle further life. This is particularly important if the Port is being held as an investment because the value will fall if the wine has seeped. Auction prices are closely related to the "ullage" - the level of the wine in the bottle.