went to a friends house for the weekend and we all were craving Q , just so happens they have a weber silver but no smoker....sooo Ive done ribs and chicken-turkey MANY times on my performer at home so I thought what the heck we don't have much to lose trying a mega cook on the grill...basically loaded 12lbs of charcoal banked the best we could to one side, some of it did end up in the center of the charcoal grate so we lit the charcoal closest to the roast first. Closed the top vent 60% and the bottom vent maybe less than 1/8" of an opening...I figured the grill would hum along probably at 325 with little problem for 8 hrs or so, however stubborn roast locked in at 170 internal for a while ( roast was 13-14 lbs I believe) grill temp fluctuated from lowest 250 to highest 335 but overall temp was steady ( no water used)....started this project at 6 pm and FINALLY finished at 8 am the next morning at 192 internal...roast absolutely fell apart wonderfully, good bark so we chopped it up for lunch...amazed how long the grill lasted with a few bricks to spare even 
