Here in Australia the mining industry makes extensive use of prefabricated transportable buildings called "dongas". They fit on the back of a truck so they are not all that big but some of them can be quite luxurious inside. They are used for all sorts of purposes including site offices and accomodation. I'm sure my fellow Australian forumites will know dongas well, in fact I wouldn't be suirprised if they have all stayed in a donga at one time or another. I have and they're alot better than some alternatives I can think of.
Here a couple of links as examples of what dongas are like:
http://www.hollingconstructions.com....ange.php?id=13
http://www.demountablesaleshire.com....tos/index.html