I built a collapsible air deflector for pulling our 29' fiberglass trailer. It pushes the air both up and out. We made 2 trips to Florida without one for comparison to the last 2 years with it. We improved our gas mileage by 18.1% both years and saved about $300 each year. I redesigned it and hoping to get up to 25% improvement for this year's trip. 218-330-9507