I use my Primo Xl for pork shoulders on a regular basis. If doing a single shoulder, I use the divider to limit the charcoal to the left side of the firebox (filled to the top of the divider) and set-up for an offset cook to the right using a single deflector plate on the right side. I use a drip pan on the deflector plate, add apple juice, insert the grill "feet down" and place the shoulder directly on the grill. I normally cook at 225 deg.
An alternate set-up uses an extender rack and decreases the evaporation of the apple juice is to use the deflector plate, insert the grill "feet up", put the drip pan and apple juice on the grill rack, put in the extender rack and then place the shoulder on the extender rack. This raises the drip plan off the deflector plate and helps keep the apple juice from evaporating.
There are pictures of both set-ups on the Primo User's Forum.
Bill