Building No 54

I think a stationary caravan that has been totally stationary for at least fourteen years (seen on many a dog walk in nearby village) could be called a building.
This type of mobile home always appeals to me: tiny, rounded, and just enough space to boil a kettle, make tea and sit listening to the rain clacking on the roof.
There is a house nearby - I assume the owners of the caravan live there. Perhaps this separate dwelling unit was an overflow for parties/kids den or just a separate pod for someone wishing to escape the main household for a while.