So I've got a brand new modern day dresden campaign starting up and one of my PCs wants to be based out of a mobile home.  This brought up the question of does a mobile home develop a threshold?  To me a threshold implies someplace grounded, someplace with permanency.  Like several generations of a family growing up in the same place making a threshold stronger.  If they were to move their entire house, I would expect the threshold to reset.  The fact that its a mobile home makes me lean toward no threshold possible, but I can't find strong support in either direction.