P.S. Not sure if anyone is aware of this but the tonneua cover gas mileage thing is a miyth, It has been proven that you get better gas milage with out the cover on a truck because the wind that goes over the cab of the truck then drops down inside of the bed of the truck and creates a whirl wind effect that actually once over the cab and into the bed push's the truck forward and creating less drag....with the cover on the wind came over the cab and push on the back of the truck and rolling over the tail gat and grabbing the undercarriage and pulling it backwards ...slowing it down.
Not sure if anyone was aware of that or not lol...look it up on myth busters lol