Pork tenderloin is about the leanest pork cut there is, and doesn't lend itself too well to smoking (read: low & slow cooking). A good sear followed by an indirect grilling works well, or a higher heat cook in the WSM. In any case, don't take it higher than about 145°. Take a tenderloin too high, or cook it too long at low temps, and you'll likely end up with dry meat-- which is the reason most of the ones you see at the supermarket are enhanced.