Smoked 2 pork tenderloins for an hour and half, they came out great! When cleaning up I noticed I was able to wipe the finish off the top of the smoke box. You can see in the picture the other "damage".
That's an awful lot of creosote for 1 smoke and would suspect that your wood caught fire. No damage and not even necessary to clean as it will be part of every smoke you have.
