FWIW the NH and BAR "potato" cars from the early 1950s were classed XIH so they were considered a box car insulated with heaters. I can't recall other examples.
Bob Witt
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The Soo Line insulated some 40' wood sheathed automobile cars in the fifties, which made them XI's; ten in 1954 for use in wet pulp service (so the bales wouldn't freeze to the cars.) and 15 in 1958 with wood plug doors(!) assigned to Campbell Soup Co.
