Pork tenderloins are really not a good candidate for smoking. Too lean, not enough connective tissue, and they dry out easily. They come out OK, but nothing to shout about. I prefer to dry rub them, inject a little garlic-infused olive oil and cook them very quickly over a rocket-hot grill. If it's high quality, super-fresh pork, I even leave them a touch pink in the middle.
The "low and slow" method of smoking really shines with cheap & tough cuts of meat that are loaded with connective tissue, the shoulder or "butt" being the prime example. After numerous hours @ 225°, when the internal temperature finally hits 190° or so, all of that connective tissue will have gelatinized and broken down into the most wonderful, moist, lip-smacking goodness. There is nothing better on this earth, I'm convinced of it!