Could the tower room be the same set that they used for Davids room.
I'd be willing to bet his crystal ball that at least most of David's room is there.
The 2nd floor of the Carey Mansion/Seaview has a circular bedroom inside its tower. I think its windows are its best feature, and upon entering, you can't help but be reminded of David's room. (The first time I saw it, everyone in my group [Nancybe, Nicky, Gothick, Selby D. Pearson, PostCool1, etc.] said they'd want that bedroom if given the choice.) The upper floor of the tower, on the other hand, was never a sleeping room until recent years-- it was originally used for storage, then was locked up for years, and has now been converted to a dorm room for Salve Regina students.
Anyway, I think there's a scene in the show that uses the tower as an establishing shot before cutting to the action inside of David's room, as if David's room and the tower room are the same. But of course just because these sets share the same windows doesn't mean they're the same room, though I believe David's bedroom at Collinwood
is directly below the tower room.