Using a 1 kg sirloin roast and smoking for about 100 minutes per kg, makes for a really nice rare to medium rare roast. Preheat the smoker to 225F, apply the rub after letting the roast to come to room temperature and enjoy.
Rub:
1tbsp salt
1 tbsp pepper
2 tbsp garlic powder
1 tbsp onion powder
1 tbsp of herbs: rosemary, thyme
Of course you can delete the herbs, or increase the respective ingredients as to your taste. I also sprinkled the roast with Lee & Perrins before adding the rub.