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.

Here's a link to a NHRATA forum discussion about these cars:

http://thenhrhtanewhavenrailroadforum.yuku.com/topic/8135#.WOxTrY61tmA


Bob Witt