Wrapping your tri tip in foil is not necessary using the low and slow method. It is naturally a juicy cut of meat and cooking it at 225°F for two hours will not dry it out. Take your tri tip off the smoker when it reaches your desired internal temperature to avoid overcooking. Letting your meat rest is also important for retaining moisture! Cover the tri-tip roast in aluminum foil for 15 minutes to rest before cutting into it.