After the rain stopped this afternoon, I got my digital calipers out and measured the steel thickness in several places. It was just as I thought, the cooking chamber is made of 1/4" thick steel. So is the fire box and the baffel underneath the cooking grates. I thought that's what Ben told me when I picked it up and now I'm sure of it.
I tried to get a picture of the caliper display in the first picture, I apologize for the poor quality, I don't have a great camera but, I think you can see it reads 0.2560". The second pic is of where the calipers were when I took the first pic. Third and forth pics are for comparison of the 3rd gen to the current pic on Ben's web site.
In any case, this thing is a dream to smoke on. Just as Ben said, it'll take a little longer to get it up to temp (with practice, around 45 minutes) but, once you're there it changes temp very slowly. It holds the temp wonderfully, no dips or spikes and the built in thermometer is always within 2 deg. of my digital remote. There is so much thermal mass in this smoker it makes it easy to control temps.