Screenplay have the scene when they sleep in the truck, but so many things were changed from it Its your choise to belive it or not :D You could say they just shortened some things (like the beggining - when Ennis comes to Signal) and totally changed some, so only if you read carefully you can decide if something that happened in the screenplay was "deleted" from the movie, or simply it "did happen but behind our eyes view."
As for the barn, I dunno. He didn't hide in any sort of a barn, he just entered an alley. And he didn't look like he knew what was he doing, he just felt this things pulling his guts out, and he escaped to the first place he saw.