Looking at the big picture, in 1938 the percentages of cars in the US fleet are 40% double sheathed, 30% single sheathed, and 27% steel with the remainder of other or unknown construction.
In 1950, this has changed significantly, with only 9% double sheathed, 22% single sheathed, and 67% steel.
This reflects a number of different trends at this time. In the late '30s railroads were both beginning to purchase new steel cars in large amounts (the 1937 AAR Standard boxcar, along with numerous railroad specific cars), and they started rebuilding older cars into steel cars. In particular, old double sheathed cars were rebuilt or replaced in large quantities.
This is reflected in a steep drop from 40.3% to 26.7% between 1938 and 1942. Single sheathed cars declined much less in the same period, dropping from 30% to 28.8%.
After WWII there were a large number of new cars built, more cars rebuilt, and a lot of cars simply retired. But while double sheathed cars comprised of less than 10% of the fleet in 1950, single sheathed cars still accounted for more than 20% of the cars in the national fleet.
There are several single sheathed cars that have been released in plastic, although unfortunately many of them have suffered from unprototypical variations of side bracing, ends, and roofs. Reasonably accurate models include:
Fowler - Accurail, Life Like of Canada/True Line Trains Proto 1000
Mather - Life Like Proto 2000/Walthers
T&P/WP 50' Auto car - Roundhouse
USRA - Tichy (RTR available from Intermountain)
"War Emergency" - Intermountain
Compared to the standard box car releases, these don't cover too many prototypes.
CN/CP had a huge number of Fowler cars, but these models only match a portion of those cars.
The Mather cars are very accurate for a portion of the Mather cars, although they are lettered for a number of cars that were taller than the model. But this is a small prototype (about 10,000 built, less that match the model's height).
The Roundhouse car is very well done, and can be kitbashed into a number of other cars.
The Tichy USRA cars are good models of a fairly numerous prototype. There were 25,000 built.
The Intermountain "War Emergency" car is a very good match for three prototypes. We'll be using Larry's spreadsheet to dig a little deeper in the next post.