My ridiculous theory about the movie...

It's just my headcanon, but I get the impression that Casey's uncle killed his own brother (Casey's father).

I know the uncle did say it was from a heart attack, but it seemed a little too convenient since it happened so shortly after the first camping incident. Not to mention the Uncle seemed a little too nonchalant about his own brother dying of a heart attack during the flashback where he's all like - "it's just a heart attack. These things happen". He wanted to get closer to Casey, but couldn't do that with the father (his brother) in the way.