On most Kadey Krogens, in addition to the open masthead, you also have internal halyards sheves open to allow water in.
The biggest problem with the fresh water down the mast is rott that somtimes occurs with the floor timbers immediately adjacent to the step. Place a small amount rock salt in this area, next to the wood, as it will kill the dry rot. Salt water kills dry rott, fresh water, as in rain, promotes it.
The step may also see some corrosion, but I have not had much difficulity with this.