Knocking around ideas for a rocket mass oven.

I need a better oven to take my bread game to the next level. It needs to be cheap, functional, efficient, and be easy to remove when we move (eventually). I think the picture above illustrates about whst I would do except that I would use a brick j tube and some refractoty I have extra of to sheild a ceramic pizza stone I also have.

With the modifications you note, I think this would work fine.