I discovered a photo of a "peek-a-boo" gondola on a Facebook page. Some of you won't be able to access this page, unfortunately:
These are basically open-sided pipe gondolas, first developed by the Milwaukee Road and then imitated by the Chicago & North Western.
This is a link to a Railway Age Article, July 22, 1957, Pages 28 and 29.
The March 1957 Milwaukee Road Magazine briefly mentions the original idea for this car on Page 2:
A Jim Sands photo:
Don Leistikow commented on this photo, " The car is representative of an idea put forth by Chalie Rynsky, Traffic Manager of Globe Steel Tubes Company, located on W. Burnham Street, Menomonee Belt District, City of West Milwaukee, Wisconsin. Charlie was a well known representative in the Traffic Management field of enterprise. And Globe Steel Tubes generated lots of carload traffic.
The storyline unfolds as GST's shipped most, if not all, of its production in open Gondola Cars. Seamless tubing was its basic product. In its day, tapered trolley poles for street railway and interurban cars was just one of the many products, they produced.
Car cleaning was a constant problem and an ever increasing expense. Of course, GST management continued to prod Charlie, to come up with a solution. Ordering clean cars, does not assure that you will get clean cars.
On invitation, I was treated to a tour of GST by Charlie and found it most interesting. It was at that time, that he told me the story.
Eye-balling some of these cars, Charlie came up with the answer. He asked the MILW for a group of assigned cars, which would have their sidewalls and floors removed thus, becoming, self cleaning."
Morning Sun Color Guide Volume 2, Page 102 has a photo, I'm told.
The Chicago & North Western Historical Society had an article with photo in the Summer 1996 issue of the NorthWestern Lines magazine. I have no link for this.
I read that the car appears in Train Shed Cyclopedia 70.
Herald King made decals in HO and O scales for the C&NW car.