Dear all,
Probably you all are keeping different type of tea here. The way that i am suggesting is for Puerr Tea. As they need to breath and age. Also I might have over look on the climate in your area. if it is four season, you will need a more of air tight container. But please remember to open up the container once in a month may be... to let some air in. so that the changes can still progress.
if it is fully sealed then, the taste will not change. Anyway, the way of keeping tea is a big knowledge. Taiwan and China even come out in Magazines on how to keep Tea.
Plastic is a big NO...!! Tea absorb any smell. and by the time you want to drink the Tea, unpleasant smell or taste will be released.

Happy Drinking