We got back from a quick camping trip this morning and removed all the sand from inside the oven. Wonder of wonders it didn't all fall down! In fact it seems incredibly strong inside. The gradual arching shape of the dome means that the hundreds of pounds of weight are compacting and tightening up the walls. Although the thermal layer comprising the inner wall is by no means dry, it feels solid as rock when you rap on it with your knuckles from the inside. And it fits our extra-large 14 3/8" pizza pan easily. Four loaves of bread should be no problem.
We also did a fair bit more cobbing. We completed the first insulating layer at the back of the oven and began work on the second and final such layer. You can see the cob comes right out to the edge of the rocks at the front now.