Hey Dave. Yes it is. The townhouse was built in 1898. The foundation is "rock solid"
I actually underpinned this building to provide full height ceilings on the lower level. My crew didn't particularly enjoy removing the rear foundation wall to provide access to the yard and lower patio. It took the better part of two days.
I don't think I'll have an issue with humidity. The recess will be fully enclosed with sheetrock and 3/4" plywood, to provide a mounting surface for cabinets and equipment. This level is also climate controlled and has French doors and a large window that open out to the yard. So air exchange is pretty good. I may install a fan in a transom over the door to the room, if it becomes a problem. But I think it will be fine.