No need to brine or inject, just do your favorite beef rub and smoke to 133 IT and then do a quick sear on both sides over some hot coals. This will be a beautiful medium to medium rare.
The most important thing is to cut it against the grain, look up good directions on doing it...trust me.
Follow these instructions and you'll have a perfect tri tip.
Mini,Jimmy(Jumbo Mini),BP UDS, Kettle, Potbelly Stove Smoker Smoke house, IQ,Guru etc..Keith