It turns out that Mr. Caruso is quite a bit more adventurous than we'd imagined when he first arrived here. After two days living in the hall bathroom, he decided it was time to get out and explore the rest of the house; once he'd done that, there was no keeping him in that room. He's still scared, of course, and tends to run away whenever David or I try to approach him, but we figure it's going to take some time before he feels safe enough to hang out with us the way our two cats do.
He's found several places to hang out (under a table in the living room, on top of a set of drawers under the desk in the sunroom and under the dining room table - do you sense a theme here?) and we can usually find him in one or another of his hidey-holes when we look for him.
At this point, our biggest problem is keeping Harley and Sam away from Caruso's food (he's on a special diet), which isn't easy. But from what I can tell, he's eating and drinking and not too terribly traumatized by this latest change in his life.
I'm just looking forward to waking up one morning and finding him curled up on our bed, fast asleep. Then I'll know he's really joined the family!