Bright sunshine and circulating fresh air works miracles, BUT the bright sunshine will sunburn the sheath and it will turn a lot darker. A light coat of PURE neatsfoot on on a clean sheath would be advisable as well. Also Baking soda will deodorize the box to some extent, but I don't know if it would become a permanent part of the sheath or not. If so, the sheath is washable with mild soap ie. saddle soap and then dry completely , then the Neatsfoot application. Good luck.
Paul