After a bit of thought, I think I'd like to change the Empowerment bonus I give the castle. Instead of making it/occupants healable via positive/negative energy, I'd like to proof it against incorporeal and interdimensional travel. All of its interior and exterior surfaces are impervious to incorporeal creatures who are not bound to the Soul Casket, and the entire castle is under a permanent Forbiddance effect that can also be bypassed by creatures bound to the Casket.