What a great gift he gave you. Good job DH.
Get the charcoal from the pet store. They sell it in bags.
Set teh charcoal in a glass bowl in the bottom of teh case, close the lid, after a week open and check it. Still smells? CLose the lid and go another week. You can set it in the sun , but be careful of bad weather, critters, and the sun may damage the case if not careful.