hopefully this will be useful for those who are making Cortile Barile oven, and are close to step A-20, when you have to pack refractory in box 2. What I found out is that packing refractory well is really difficult, even with the recommended 2x4’’ stud. It might work for the inner sections of the slabs, but it might not pack the refractory in the flange areas. What really helped me is a 1’’ dowel with rounded edges (so that you would not tear Styrofoam mold) that fits nicely in flanges of the side slabs and a 3/4’’ piece of wood that can pack the refractory on the top piece in the middle of the box 2. Together with the above-mentioned 2x4’’ - I managed to pack refractory very well.
Another piece of advice - do not put a lot of refractory in the box at one time. I used 2-3 handfuls in sides and 1-2 in the middle and pack firmly and slowly after each time. It is slower (took me about 2-3 hours to fill Box 2 completely, but I mixed the refractory with water by hand), but the result was a very well packed slabs.