I too had noticed the drop in gas mileage with the roof rack on. I decided to buy a little motorcycle trailer for the things I don't want in the van. After traveling around on a few lengthy trips I noticed the gas mileage actually went up. I think the trailer breaks up the air behind the van and gives it a cleaner air line. Kind of takes away the vacuum that's created behind the square back. Just my opinion. Others mileage may vary