I wonder if they are insulated inside, outside, or both? Jobsites I have worked on use those extensively for field offices, temporary electrical distributions, tool/material storage, etc. and those that are insulated tend to feel pretty "cavelike"; might make a nice hunting cabin or fishing cottage, but a bit claustrophobic to actually line inside one, IMHO.
What is going on with those weird external shutters on the right side? I assume they are adjustable for angle to control overheating from sunshine through those big windows? Do they swing aside easily for access to cleaning the windows? Look like a bit of a PITA...