Tricky part is that those folks are likely to be closed-mouthed about it.
I've "hardened" a number of spaces for a number of people, and that's about the level of detail I'm willing to go into that.
Most of those solutions used existing building technology, just applied to suit. That's ranged from wooden studs to galvanized stud to CMU. Each solution was individually tailored to its application.
The question becomes one of goals--your goals in this case.
Do you want fire protection? Do you want more or less break-in resistance (exposed hinges, concealed latches, etc.) ? Will this need to be esthetic (as in either being "pretty" or in being "invisible")? Will you want water resistance (FD will apply water in hundred of gallons per minute fighting a residential fire)? Will you need humidity/temperature control?
This matrix is what will inform your design.