I've got a 99 SC LB 7.3 4x4 f250. Unloaded and empty hwy cruising I'm getting 18-19MPGs I'm looking to get that up as high as possible. So reading some stickys in this section air getting under the truck creates a bit of drag. I don't know a thing about aerodynamics other than it can make a truck look goofy. So I was thinking about making an air dam that's removable or get real fancy and do retractable with hydraulic arm or just a hinge fold up. I'm thinking maybe two or three inches off the ground and only use it on the highway. Does any body have any suggestions for material? Maybe just thick rubber pad or plastic? Or a steel/aluminum frame wrapped in vinyl.