Espee's " Sugar Beet Gons " started life as plain old General Service composite gondolas. I recall they were originally constructed before World War 2, when the use of wood sides was still common, especially in equipment such as drop - bottom gondolas that were subject to hard use. (The wood was easier to replace than steel.) The use of wood in the sugar beet extensions was therefore an easy, and cheap choice. It's worth noting that some of the " racks " were raised with plywood sheets.