What are these trailers?

Unless they are trying to keep them hermitically sealed and totally climate controlled in some way?

 

No.
Still doesn't add up.
Look at reefers.
How many off those have threaded locks?

 

It's a refuse (garbage) trailer. Here's a picture of one without the extra doors and axles. States like MI, OH & NY run extra axles for more weight.

http://www.truckpaper.com/ListingsDetail/Detail.aspx?lp=TRK&OHID=190477527

 

This. My buddy caught up with one at a rest stop on the 90 in NY a year or so ago. They were hauling Aluminum out of port of Oswego to Michigan for at least Ford if I recall.

 

No , they are definitely not garbage haulers. rear doors are different

 

They are set up to haul coils into a facility, and haul scrap clippings out.

 

My company pulled one last year, but it was a Mac 45' spread flat/dump. Pretty cool, but not the lightest. If you got really mad @ receiver I guess you could dump your coil!