The brisket acts as a heat sync and will cause the element to come on more often than an empty smoker resulting in the wood burning better. The manual recommends an empty smoke. Most here at the forum would recommend you smoke a pork butt. It'll season the smoker better because of the heat sync concept and all the fat from the butt.
Come to this forum for info rather than relying on the manual. LOts of help and good info from experienced folks.