Did some more reading and it looks like summertime smoking in a Weber kettle works just fine, although you might have to check on it more frequently. Wintertime is what I'm not so sure about -- the WSM bullet seems to have thicker walls and is reported to work well in the winter while the kettles seem to be iffy for anything except grilling (where you can have a full bed of coals). I think the fact that the WSM can run with a full basket of coals even when smoking might be part of the difference.
I guess the real answer is something like this :
http://www.bbqs.com/cart_admin?func=viewProduct&wid=78&cid=1047&pid=12561/4" steel walls, 350 pounds...
