Fire up the BBQ smoker and preheat it to 225°F / 110°C. Add wood chips, chunks to smoker and let everything become nice and smokey.
Place tomatoes in single layer on a baking tray. Smoke the tomatoes for about 20 to 30 minutes. At end of smoking time, carefully remove tomatoes from smoker.
Add smoked tomatoes and pan juices to large saucepan; heat on medium-low heat. Add shallots, 4 tablespoons brown sugar, vinegar and celery seeds; simmer, uncovered, 2 hours or until reduced to 4 cups, stirring occasionally and breaking up tomatoes with a potato masher. Remove from heat; cool.
Add tomato mixture to blender container. Cover; pulse on and off for 1 minute or until smooth. Return to same saucepan. Add remaining brown sugar, salt, cinnamon and allspice. Simmer over medium heat; reduce heat to medium low. Simmer 30 minutes to 1 hour until reduced to 2 cups or desired thickness. Remove from heat; cool. Pour into sealable glass container and refrigerate for up to 1 week.