Hate to give away one of my best tricks, but ...
Build a doorway and put a door in it that swings out below the access to the floor above. Put a small box just beyond the edge of the door when it's open. Make sure the door has a lock on it.
When the door is open, you can jump from box to the door to the next floor up. Close the door and now the upper floor access is gone. With a cupboard up top, you don't have to remove and rebuild your stairs all the time as the door acts as a gate to the floor above. Raiders can remove your door but can't add their own.
I used to do something similar but it was a little bit clunky so I gave up on it. Your solution sounds a little more elegant however, and while it isn't as smooth as simply running up some stairs, the advantage of the removable "stairs" might compensate for this.
Time to fire up my test server to experiment. Thanks.