I think you guys are over thinking this. The main driver behind transfer cabooses was cost. Both the operating rules and union agreements said that transfer moves needed cabooses; if there were not enough old cabooses surplus from road duty available, something had to be built. The requirement was a small shelter, with a stove, some benches and a desk for the conductor. That dictated a small body, and early in the century a four wheel bobler caboose would have filled the bill. But four wheel cabooses were fund to be unsafe, and were outlawed sometime in the twenties, IIRC, and that meant a small cabin on a long frame. Converted boxcars were rather common up until WWII, usually rebuilt from cars that weren't much bigger than a standard caboose. But by the sixties, when these "cheesebox-on-raft" transfer cabooses became common, the available boxcars were way too big to be heated efficiently. Some of the early examples of the style were rebuilt from boxcars, leaving the center section of the body and building new ends, which yielded large porches which didn't need to be heated. Later it was found to be cheaper and easier to just build a new body and mount it on whatever surplus frame was available. Not exactly rocket science.

The lack of cupola was to reduce cost as much as anything. Nobody was much worried that these slow speed moves were going to develop hotboxes, and in many environments anyone riding in the cupola was going to become a target for rocks or worse, so nobody was riding in the cupola anyway. Why maintain the windows? Sometime in the sixties, early seventies the Soo Line did just that; a bulletin went out to the RIP tracks that henceforth broken cupola windows in cabooses in transfer service were to be boarded over. Some few of these cars subsequently received new plywood sheathing, and the cupolas were entirely sheathed over, just a square blank box on the roof. Some roads, like the Chicago North Shore and Milwaukee simply removed the cupolas and filled in the roof sheathing. I'm familiar with one of their cars, CNS&M 1002 at the Illinois Railway Museum, and all the lockers and the ice box that were under the cupola floor remain; the space between the former floor and new roof was good for stowing grips, etc.

Dennis Storzek