this was really technical and difficult to do.
there are real limitations on what Navigation2D can do, and i reached them tonight.
Godot 4.0 addresses these limitations, though it is still in beta, so i wrote some custom “set walkable and blocking tiles” logic.
This fence walls off the camp except for an entrance on the south west corner.

I also realized that fully blocking in the camp means players would be stuck!
I think this is fine, they can just fence themselves in right before night time, and remove the fence pieces each morning.