I have seem logs, big logs, stored outside, off the ground, in the shade, for a year plus, in as long a length as possible. My theory on this is that they are getting rid of the moisture down to a point. Then the logs are carted off to be dried inside i think, or kiln dried, before any mold fungus sets in. The outside enviroinment seems to slow the drying and keep the outsides moist, whilst the inside dries. I have also seen trunks sawn into boards and then stacked outside one ontop of another with spacers inbetween the boards, but again it seems to be a case of slowing the drying out to stop warping or cracking. Be sure the fungus dooesnt get in though, i think this is when the wood begins to rehydrate!
Edit:
Thats undercover from the sun though, id let them get some form of moisture to the outside. The full lengths i have seen probably loose as much as yours from either end i must add through radial splitting.