What is the importance of Charles' Mercedes in the novel, The Wangs Vs The World?

Much of the novel, at least for most of the Wang family, takes place within the confines of an ancient Mercedes that had once belonged to Charles's first wife, May Lee. The Mercedes has been well cared for, despite its years, and is still in pristine condition until it undertakes the road trip with the family. As they drive, the inside becomes littered with Grace's clippings and the family's trash, while the once-pristine paint job of the car's exterior becomes covered with dirt and dust from the road, its top coated with a layer of bird droppings. The car is a claustrophobic space in the midst of the great openness of the American road, and its slow, continual disintegration mirrors the collapse of the family's fortunes.