Read the book.... or watch.... IT will be interesting to see how close this track the story in the book. I could tell you why the Propane is there per the book.... but I won't!
Specifically, it was a nosey-neighbor type who called the police (!!) to report an excessive number of propane trucks going in continually. The implication has to be that this was a planned thing. I haven't read the book so I have no idea if this is the case.