Did one yesterday, an 8 pounder. I like to do the garlic in some slits rub with olive oil and then heavily salt and pepper. I like to dump in about 15 lbs of charcoal in the side box. :Let it get rip roaring until about half the coals are going. I always light the inside edge closest to the grill box, so the fire works back toward intake vent. I put it on when the box is about 425 then let ti go for about 30 minutes before clamping down the dampers. Letting it fall back to 300 or so degrees.
Temp thermometer a MUST. I usually pull about 125 or 130. Outside edge smoky but still more like a traditional roast in the interior. UMMMM... good... horseradish sauce is a must!