I just did racks of lamb back ribs yesterday for the first time. The 1-1/2 lb package of two small, well-trimmed, chilled slabs went a 4-hour cook, a dry 2-hour apple smoke, 225F, one slot over a sheet pan of water. Basted at two hours and again at three hours. The consistency was good - crisp on the outside, and acceptably moist inside. My spices for the dry rub might have been a little too aggressive - brown sugar, garlic powder, sumac, fresh ground rosemary, Colman's dry mustard and S & P. The basting/glazing sauce was diluted honey, a little soy sauce and black pepper. Next time I might try rubbing the racks first with a little Dijon mustard and season with just the garlic, rosemary and S & P. For the basting sauce I will stay with the diluted honey, but just add S & P to keep it neutral tasting. It is definitely worth doing again and experimenting with, in spite of the racks not being cheap (almost $12/lb). I found the 1-1/2 lb just right for two - the bones are quite small (thin).
It's best to slice the racks tight against one edge of each bone with the blade angled toward the outer side to leave all the meat together on the other side.