If you watch the 1960's movie "In The Heat Of The Night" there is scene
that features a Missouri Pacific train passing overhead and there are three
gondolas filled with containers that look remarkably like the Athearn "box"
style containers. The other cars in the train are covered hoppers so I'm
going to guess this train is moving cement cars. (It was filmed in Illinois.)
But I agree with Ben there were some insulated/LCL containers that also had
a similar appearance to the boxy Athearn containers. MP operated a number of
different kinds of bulk and LCL containers.
I've only ever seen the cylindrical containers in LV gondolas. I bought decals
for them from someone here years ago -- although the name escapes me now. The
gondolas can be "stood in" by modifying the Athearn gondola to remove the deep
fishbelly, cutting holes in the side, and putting steel braces on the floor and
top chord to hold the containers in place. You can detail the containers to
greatly improve their appearance, especially the lifting lugs.