tri tip as brisket

If you Inject, you can introduce surface bacteria to the center of the meat. For safety smoke at 225°F or higher. At 180, you risk the center being in the Danger Zone too long and bacterial toxin build up can make you sick even if the meat cooked until the bacteria die at 165°. Tri-Tip while tougher than Tenderloin or Rib, still has less connective tissue than Brisket. Since the Gelatin from connective tissue plays a big roll in how Juicy very well done meat feels in the mouth. Smoking Tri-Tip to the point of Brisket can result in a tender but extremely dry cut of meat. This is why there are hundreds of posts on Tri-Tip Med/Rare or Medium and few with good results cooking it further. You can do it but the window of perfection is very small. Be prepared to turn the dry beef into Chili  or some other dish. A better cut to cook like a Brisket is a Chuck Roll or meaty Short Ribs in one rack. I would not risk it...JJ