i did a 7lb flat last weekend. put it on a 22" WSM with temp in the 260-ish range fat side up. i checked it at 6 hours and much to my surprise it was probe tender and internal temp was 195. So i pulled it, wrapped it in foil and placed it in a cooler and covered in towels. Carved it about 5 hours later and it was still hot and very juicy. i usually do whole packers but could only get a flat that day. no injection just dry rub.
Al - CG SuperPro w/SFB and Outlaw w/SFB, 18" WSM, 22.5" WSM