Can be done, has been done in innumerable ways. Today's NY Times had a story about one of these: http://www.nytimes.com/2009/07/16/ga...ntainer&st=cse
Not so sure if I would like it as a living space. They are only about 8ft. wide and can make a shotgun shack seem roomy. By the time you finish things off and install all of the comforts of home, it's not much more work to use more conventional building methods as mentioned above. The best thing about them are the speed and portability for making work space. Set them on a flat piece of land, swing the doors open and your ready to go. Electricity and water source is a plus as is an outdoor shade awning. Working inside of one of these is like working inside a marching drum if you're using power tools. My preference is for the 20ft models. Easier to move and place even when loaded with a couple thousand pounds of tools and materials. If I were to get a 40ft, I would definitely get it with doors at both ends. The other upside to these is that they're typically not considered buildings and are not taxed or require building permits in most municipalities. Don't know how living in it might affect that. Back to the speed and portability......if having these runs afoul of local ordinances, you simply pick them up and move them. They tend to hold their value for resale unless you cut them up and reconfigure it crazy.