The outerwear lids are good, but they WILL NOT keep all the water out of the box. I run that setup on my mx quad because some track owners water the tracks excessively. It does a great job at helping keep the water out of my air box. But if I hit A LOT of water (like you do in XC), it WILL get into the box. I would stick with the airbox lid. The little extra power that you would gain is not worth what you would be sacrificing. Just my opinion.