If you read the PDF, you will find they are the work areas for military equipment repair. Yes, there is room inside to move and work, and to bring equipment in and out. Single-wide vans are used for smaller equipment & work stations, larger ones have double or triple set-ups.
Those illustrations of the sides coming down are not what you thought they were... they are not every-day accesses. They are showing that you remove the panel or side, then bolt it up to another module (with a rubber gasket between). The ends fit together to form those complexes shown... so you only use one external door to access 15-20 vans.
They are weather-proof... they are used regardless of weather... snow, rain (how does 6 inches in 2 days sound*)...
I spent 5 years working inside them, while in the USMC... repairing the avionics from Marine aircraft.
They have been where the USMC has much of its support equipment since the early 1970s, allowing a squadron to pack up its support & repair capability and fly it all around the world, and have it up and running within hours-days.
In 1984, we packed up from MCAS Iwakuni, Japan and flew to NAS Cubi Point, Philippines*... stayed for 6 weeks, then returned (personal example).
*May/June in P.I. is the start of the rainy season
For Traveller use, the AC/heating units can be set up for internal mounting (should be much smaller at higher TL than the 7 these are), and you just make the end module be an airlock/decontamination station, and they will work in hazardous environments.