Take the beef roast and start cutting 1-inch (2 1/2cm) from the base. As you slice, roll the roast beef away from you so that you continuously cut an even thickness of the meat.
Season the beef with salt and pepper; rest for 45 minutes for the salt to react with the meat.
In a small pot add the chopped onions, sage, and white wine. Simmer until the onions become very soft and fully transparent.
Using a fork, mash the cooked onions and sage with the butter until relatively smooth. Leave to rest until the beef is ready.
Preheat the smoker to 225 degrees F (107 degrees C).
Lay the beef flat on a chopping board. Evenly spread with the sage and onion mixture, leaving a gap at the end that you plan to finish the roll at.
Start gently rolling the beef, if done too tight the filling will be squeezed out. When rolled sit stably on the join.
Layout lengths of butcher's string to evenly cover the beef roulade. Place the meat on the string then evenly tie each piece of string firmly but not too tightly. When ready lightly sprinkle with the beef rub.
Place the roulade in the smoker, this can be done directly on the rack or in a roasting pan. Cook for 3 hours but start checking the internal temperature at about 2 1/2 hours until the temperature is your desired doneness.