Describe the U-Haul story. What is the importance of the story?

While driving to Battle Mountain, the family rents a U-haul to carry their things. Unfortunately, this means that the children have to ride in the cab of the U-haul, hanging onto the family furniture, and without any light. During the trip, the back door of the cab opens. Rex is alerted by a passing driver and pulls over. This event is significant because Rex gets mad at his kids.... like it's their fault they've been traveling in a dangerous manner.