Troy. I went and got a cup of coffee and it came to me, another idea I had when I wanted to build an oven......again, similar idea to your barbie.
I didn't want to put in footings cuz where I wanted to place the oven was already paved and the thought of removing quality concrete was more than I wanted to deal with. So, as I investigated the kits mentioned in "oops", it came to me that plate steel could solve the problem. Of course, I have a friend who has a supply and loves to weld 1/2" steel together. Bottom line, I could build the project very resonably "and" if I wanted to face it with masonry, a steel ledge along the base could allow for the addition of stone or what ever. However, being into "designing" stuff, I drew up add-on steel details that made it look like outdoor furnature......sort of "craftsman" style table if you know about that.........and I could paint it, like a Weber, or let it rust since it would take you another milinium to rust away, or cover it with stucco, like the behive forementioned, with steel studs and metal lathe....personally, my preference. Basicallly you would be building an "insert" just like a fire box.......except the insert is the final product. Now this puppy is not exactly portable, but it would have solved my needs.....cheaply.
I bring all this up cuz you seem to be trying to stay away from masonry construction. If you don't have an adversion to masonry construction, make sure you give it a good look too.
And,you know, the cost to build these things can be a little costly. As I watch HGTV and see these professionals cooking, they don't use "in-place" bar-b-ques,but put their money into a "covered" space with the proper work place for cooking, and "buy" a quality bar-b-que unit from a reputable manufacturer. If the pros use these things, perhaps they know something we don't.....!
Aren't projects fun?
Good luck, Troy. Once you get your bar-b-que up and running, call us over for surf and turf. BEG