Not a full answer, but there are several traditional ways to prevent logs rotting in a cabin:

1. site the cabin on a natural rise in the land to drain groundwater away
2. plant shrubs and other vegetation nearby to soak up standing water
3. compress the earth foundation both for flooring and to prevent infiltration
4. build the bottom course of logs on top of flat stones and seal them with clay or pitch underground - logs will not rot in an anaerobic environment
5. build the roof with large (5-8 foot) overhangs to cast rainwater away from the foundation
6. dig small trenches to direct rainwater into a cistern away from the foundation

A combination of most or all of these will keep the house as dry as possible and should prevent any wet rot from occurring in the first place.

Another style was essentially a roofed pit in the ground, especially where resources were scarce. In this case, a small berm would be built around the pit to prevent infiltration, the walls would be lined with clay if possible, and the roof would be a stilted frame anchored in the berm with a large enough overhang to cast the water away.

To add a little to what BullMoosePartyAnimal has said: whitewash ( a simple water-based paint of slaked lime with a little milk) was very common. It deters boring insects, helps shed water. It also had the virtue of making the cabin look more like one of the clap-boarded houses in town.