As I understand it , the price of that setup at Costco, is cheaper than other places sell the LG900 alone.
I think they sell that smoker box separately for other grills, in the add on thing, it has two wheels for support on the right hand side... the setup at Costco doesn't seem to have any support at all on the right hand side, surely that's not such a brilliant way to go, no support at all for that big smoker box???
Having said that, the price is so attractive, I'm sure a person could find a reasonable way to support it with some sort of home built legs or something.