Depends on how hot you plan on cooking at. I consider smoking birds to be the hottest temps that I'll cook at, and at times run up to 325* for those, and I season at least 50* hotter in case of temp control issues during smoking. I go to at least 375*, bringing temps up slowly for about 3 hours, then hold for an hour+. For a large rig, temps that hot may not be achievable even with somewhat of a runaway fire...but it wouldn't hurt to see it reach at least 300* if brisket, ribs and pork shoulders will be your main smokes.
Eric