Combine brown mustard, garlic paste, horseradish, yellow mustard, and worcestershire in a small bowl.
Brush evenly on the rump roast.
Combine salt, pepper, paprika, cumin, chili powder, and onion powder in a small bowl or ramekin.
Season the rump roast by dusting or rubbing over roast.
Place the roast into a large pan or casserole dish. Pour beef broth and beer around the roast into the pan.
Place into the smoker and smoke for 3-4 hours. The liquid will steam as it heats keeping the roast moist and tender while infusing with flavor. PLEASE NOTE: It may take longer or go quicker in your smoker so please only go by the internal temperature of the meat not by actual time (it's just a general guideline).
Remove the roast from the smoker once the internal temperature reads about 135F degrees (for medium doneness). Remove roast from the pan and let rest for 15 minutes, the meat's internal temperature will continue to rise a little bit as it rests.
Remove roast from the pan and let rest for 15 minutes.
Pour the liquid into a saucepan and place over medium high heat. Heat to a boil, then remove from heat. Serve alongside the roast.
Slice and enjoy.
Notes
I used a 3 pound roast.
Make sure not to forget to pat your roast dry.
Use your judgement on the mustard. You'll need enough to cover the roast. If you don't like brown mustard, just use all yellow mustard and use as much or as little as you prefer.
It's very important to let your roast rest after smoking. You don't want all the juices pouring out from cutting into it too soon. Letting it rests allows those juices to really reabsorb back into the meat and they won't all come using out when you cut into it.
You can use a pale ale or a pilsner beer for this. If you don't want to use beer, you could use additional beef broth.
When smoking meats you MUST use a meat probe (or meat thermometer). It is the only way to tell when the meat is at your desired doneness and not overcooked or undercooked. I cannot stress this enough!
TEMPERATURES FOR MEAT:
Rare: 125F degrees, medium-rare: 130F degrees, medium: 135F degrees, medium-well: 140F degrees and well-done: 160F. I pull it off when the internal temperature reaches 135F degrees to get a medium doneness. Remember the temperature will continue to slightly rise once it is removed.