I just talked to a guy that used to work with this oil storage system and he said they would turn the drums like a wine bottle every month or so. Otherwise the additives and the waxes in the oil will drop out with the water.

Storing it flat on the floor will cause the bottom to rust out and that is why they stored them on their sides. The slight elevation was to drop out the water, and the monthly turning kept them mixed.

But they did have to turn them back to the right direction in order to draw from them, but how often will you be drawing from the drum?

He estimated the shelf life at three years.