Watched an extreme houses or similar program where the guy used connex boxes to build a house. One of the issues he found was the strength was on the edges and he had to reinforce all the walls, top and bottom- especially when cutting holes in the sheets.
Spray foam (2 part professional) and skinning on inside or outside would make a huge sound and isolation difference.
If you use rubber body mounts or something similar to isolate it, could help with vibrations during travel or while running genny, etc.
A generator/refridge unit over the cab might be nice for power and A/C ;)
Don't forget the slats in the windows and turret on top! :p
I think it is a cool idea ;)
BTW, might be interesting to use a dumpster loader style truck and then make these as "deployable living" for seasonal or long term living ;)