The BRP G4 seat storage box (860202532) fits perfectly on the G5. Obviously, I have the small gauge but my buddy with a large gauge also added this box to his sled and mounted the battery in it. Either way, it helps out with storage in a big way. I'm able to fit my overpriced BRP tool kit and all my other heavy rescue gear in it. My spare belt fits nicely in the bottom of my tunnel bag. I'm not seeing the box on the Skidoo website, but there seems to be plenty available at dealerships.