I was eight when this was posted, sorry it took me a bit
I don’t know if this is still relevant to the OP but for those who may end up reading this thread, I’m not going to discredit any of the proposed solutions, however, assuming I didn’t miss anything, I think something critical in the original post has been completely ignored.
… wood stoves.
Wood stoves heat a home via convection, which heats the air and moves it throughout the room. When the warm air hits a cold surface, like cob or stone in the winter, the water in the warm air condenses against that surface. The problem I’m seeing here is the way that wood stoves heat rooms, unless the surfaces of the house are insulated from the drastic heat difference outside the house, you will always have water condensing on said surfaces.
I’m proposing that this problem could be mostly or partly caused by the use of a convective heat source instead of a radiant heat source (like a rocket mass heater which anyone who has spent any time on this site would have some idea about). I would suggest finding some way to heat the cabin (or whatever space the inquiring viewer wants to heat) using some sort of radiant heat source in contrast to convection.