The advice everyone else has given you about temperature is good. As long as you don't overcook it, you'll be fine. And if you do choose to brine it, make sure it's completely dry before you smoke it. Otherwise the smoke won't cling.
My only experience smoking pork tenderloin is using a stovetop smoker. The meat is rubbed with olive oil and thyme, then cooked for 25 minutes in the smoker over medium-high heat. They say that is the equivalent of 375 degrees F, so if you are using a grill, figure what level that works out to (sorry, I can't, since I don't have a grill
). In any case, it comes out very moist, without brining.