If it was built with cedar, it would have been more resistant to the mold. There is something to be said for building with native materials.
Any extra venting will be negated once the cabin is buried in snow. as long as the cabin doesn't see regular use, condensation will always be an enemy. No matter how tight you seal a building, humidity will always find a way in.
Another thing is that the insulation should be on the outside(cold side) of your vapour barrier. This goes for both the roof and walls. It wont stop condensation completely, but it should help a bit. The Floor shouldn't be sealed, as any moisture that gets in there, needs a path to exit, or you will have mold growth.
Another option is just use the cabin more……..What could possibly go wrong?