When it comes to beef personally I'm a big fan of SPOG (Salt, Pepper, Onion, Garlic). If you are going to apply the rub the night before, leave the salt out until just before you put it on the smoker. Salt will draw juices out of the meat.
I have made a paste before of Pepper, Onion, Minced Garlic, Rosemary, Olive Oil, and Aged Balsamic Vinegar. Rubbed it all over the roast the night before, wrapped in plastic, put in the frig overnight, removed plastic, then added salt just before putting it on the smoker. Turned out great. Family gave it rave reviews.
I have another recipe I created that uses Thyme, Basil, Rosemary, and Sage, along with some of the ingredients above. I didn't care for it as much. Two many herbs.
With a sirloin you are only going to take it to 125F-135F internal temp (IT), so no need to wrap. Let it absorb all the smoke it can, running your smoker at 225F or so. A 6 lb roast will take 3-4 hours or so to reach the desired IT.
I see this is your first post. Stop in over at Roll Call and say "Hi." Folks love to greet new members.
Have fun!
Ray