Scored mine at the farmer's market. Bout that size. You can just make it out in this pic, bolted to the front of Biffy's skid plate, there behind the front wheel, with snow on the lid. Makes a nice water tight grub box. Holds my jerky & cheetos & corn nuts when camping...

Eight bucks, as I recall.
One more reason why Biffy Bullfrog is the best bike ever. Bolt on anything you want, you can't make her any uglier.