You Hide Them in . . .
They told me they hide them in old rail road cars or RR containers that they put building fronts on them. They also lay track up to the car to easily move them. These guys told me that keep their trains at a place called a train park. They have 20 acres with track and little cities. They go out on weekends and drive the trains around on it. Some cars you can ride in and others do "work". That means they have orders to deliver pretend goods here and there. They also told me that they usually spend 2,000 per car. One guy admitted to have 30+ cars hide in various spots.
That would purchase a whole lot of yarn.
Also imagine a yarn stash container the size of an old RR car.