Dampness in a Log Cabin can be caused by the dampness in the air. If the floor is not down yet it maybe an idea to install a DPM atop the base.
Depending on what the cabin is being used for air vents are also a good idea to use in the cabin. However, if the cabin is being used all year round then you should be opening and closing the doors to circulate the air flow, so they are not always needed.
Whereas, if the cabin is going to be used as a summerhouse/storage where it will be closed up during the winter months, then we would recommend to add these. If you are also using items such as a fridges or a hot tub. Then adding air vents will help the cabin to cope with the moisture inside.
We would also recommend to treat the inside of the cabin, as this will also help with any damp that might be occurring inside. We offer a good treatment for the inside of the cabin, this is the Impregnation Fluid, please see this below: