It's majorly thick steel. Every 3-4 cooks I pour a cup of bleach in the bottom of the water bath and just hose it out.
Yes, you can get just a good low and slow cook with no added hardware, but with this guy I can set the bottom vent at 1/4", spend about ten minutes getting the top vent right, and just let it run by itself.
Then six straight hours while the temp slowly oscillates between 215 and 240, and never have to touch either vent once. If you can do that with a pile of coals and a pan of water, my hat's off to you - I never could.