I'm generally pretty astounded by how many people end up killing themselves or others this way every year. It's a fire, don't stick it inside your highly flammable tent. Fires and things in which you've had a fire should always be left outside as they'll still be chucking out gases, and with charcoal fires they can still be burning somewhere without much noticeable heat. I spend a lot of time camping with all manner of fires, stoves etc (historical re-enactor) and I've never once thought "I should bring the fire box inside the tent so it doesn't get wet". Keep your burning materials in the dry, and the box/BBQ/whatever outside.