I had the same problem with my "250 Gal Oil drum Smoker" (search for this upload). Mr. Dave mentioned, to lay firebrick on the bottom of the FB. This worked Very well. But, I wasn't getting enough air to the back of the box. So I made a grate out of angle iron, and placed it directly on the firebrick. This was MONEY! The temp is more controllable and the fire burns constant from the front to the back of the FB. Mr Dave, nailed it.