Hi, Steven
I seem to be picking up a vibe where you have the desire to add caboose cupolas to various kinds of equipment, based on some of your business car/locomotive/cupola threads of the past.
I can relate to that, to some degree!
PRR_line2 by Edmund, on Flickr
Many, if not all of my "kitbashing" projects come from sort of a conflagration of ideas combined with opportunities that seem to fall into my lap.
For instance, this PRR MP54 that is getting the cupola "dome-car" look. As it happens, I found a deal I couldn't pass up on this powered, Con-Cor, MP54 and it just so happened that I had a left-over roof from a PRR N8 cabin car.

After doing some research and planning I discovered that the Pennsy had several of these line cars, many of which were made from former "doodlebug" gas-electric cars but I beliece I found photos of some that may have been MP54s.
PRR_line3 by Edmund, on Flickr
As you can see, the cupola is a pretty good fit to the roof contour so making the final joint will be effortless. The pantograph did not provide any power to the car but was raised to ground and insure the 11,000 volt AC, 25 Hz. overhead catenary wire stayed de-energized.
PRR_line1 by Edmund, on Flickr
This is about as far as I got with the project but now that you have re-kindled my interest in it I'm ready to dive in again. I have the PRR yellow M-of-W paint and decals.
Shorpy recently had a photo posted by William Volkmer showing the top of a PRR Tower car:
http://www.shorpy.com/node/23153?size=_original#caption
You can see the pantograph raised just beyond the crew. I plan to make some wood platforms for my version of the car.
In the meantime this photo kind-of shows a similar car to the one I'm making.
http://www.railroad.net/articles/railfanning/worktrains/media/MW_18.jpg
In the above photo you can see a slightly-narrowed cupola, used for wire inspections, on the roof.
My scratch-build/kit-bashes have to at least be plausible if not quite historically accurate.
Cheers, Ed