Can you elaborate on that? Structurally they're quite a bit sturdier than typical residential construction. You need doors and windows, but that's a matter of cutting holes with a plasma torch. You can use 2x2 and foam board on the inside, and partially bury them in earth for the bulk of insulation, while running ducting, etc. under a raised floor. You certainly have limited space layouts--a CalKing bed ain't fitting--but that's not necessarily a deal breaker.

Personally, I lean more towards Quonset huts for inexpensive and durable construction.