I work/live the Afghanistan area of operations. We use tons of shipping containers/connex's for everything out here from storage units and housing to offices and latrine units to bunkers. They are ultra modifiable and you are only limited to your imagination and ingenuity. Hell I am sitting in a 20' right now that is my office. The doors have been taken off and a wall with a regular 30" door put in. The interior walls have been studded with 1"x1" and use a 1/4" compressed dense board for wall covering.
I consider them to be the best thing since sliced bread and I use them throughout theatre for bunkers around our living and work areas. My experience has been that if you plan on putting any sort of weight on top of them besides another connex you need to reinforce the inside to support the weight. My bunkers have a 2' minimum thickness of dirt on top and without the support beams and columns would cave in a 20' connex in a few months.
I have planned on buying a few (2-4) 20' connex's when I get home and burying them into the ground, welding them together, creating doorways from one to the other and compartmentalizing them for storage, living, and common area space to sustain short term living. I have even considered creating an indoor latrine tied to a septic system. Going over plans in my head I would ultimately like to coat the container in a bed liner type material to seal it from moisture. I have plans on excavating into a hill to set them and then recover with earthen material completely except for the entrance and would love to have the entrance disguised as a small hunting shack.
With connex's, an assortment of 2x4, 8x8 and 1x1 a few cheap premade doors, some pvc pipe, romex, outlets and boxes, basic hardware and some sort of rented excavation equipment the options are endless. The hardest part will be setting them in place as it would require a crane of some sort to lower them into place.