I worked for several years in a portacabin, although as they called it a 'modular office block'.
It was probably posher than the type of thing that you have in mind but ours was insulated and heated and to be honest once you were inside you really couldn't tell you were in a portacabin at all.
I would think that if you can get it moved easily enough and the cost of the cabin and the insulation and heating ins't prohibitive then I would go for it. I am sure the lad would appreciate his own space.
Sally