I've heard about how large temperature swings can affect ammo by shortening its shelf life. They say you shouldn't store it in a garage for this reason. But what if those temperature swings happen only a couple times a year, and the ammo is below freezing half the time. Specifically, how would ammo be affected if it were buried underground in a moisture-tight container in a northern climate where the temperature gets well below zero at night? I'm hoping the affect wouldn't be too bad since the temperature changes slowly underground. But what about being frozen for so long?