the idea of a dewpoint within the logs is an interesting one that seems tough to solve. logs do allow moisture through, but like Derek says in winter the vapour will not be evaporating off the outside. perhaps the closed-in, wrap-around stave-work porches on scandinavian buildings would move the dewpoint further out and protect the logs. it's more likely though that the long-surviving scandinavian log buildings allowed moisture out through drafty doors and windows- or even the smoke hole in the roof!

another time-tested way to preserve the logs would be to hew away all sap wood, either by squaring or making ovals of the logs, as the norwegians did. also turning the checks down, as the Cordwood Guy says, and also the little detail of hewing the timbers upside down so when they;re flipped the cut edges feather down.

as far as water from the outside goes, in log design its all about the big overhang. that seems to be a recurrent difference between log and timber structures. in a log home it is worth the risk of exposing plate logs and rafters by extending them to carry the roof out to protect the corner-work, lower logs, window and door openings, and sills. by contrast many roofs on timber frames have little overhang (and look to my eye like too-small hats) because the structural members are generally wrapped up inside the building.