I would also throw in a vote for the Grain Door Bundles.
I do not have the paperwork handy however if I recall correctly, in Duluth, MN had a...I will use the word "consortium". Not unlike where several railroads supported a Union Station and together underwrote the costs of the station operations.
As I recall, just like soda bottles in the days we model, these door had a "deposit" associated with them. Two dollars for grain doors and four dollars for coal doors. On the line I have studied for modeling, this lead to cars returning to Duluth on occasion from flour mills on the line not with a hand full of doors, rather a few hundred from the busier mills.
I believe all the railroads in Duluth/Superior used this firm to repair the doors and to serve a central repository to store the doors until needed.
If I can find the paperwork, I will post it. Jim Dick - St. Paul