I continued to build up clay around the hard clay positive until it was halfway up the model (This will later become the parting line). I then trimmed the saran wrap at the midway point and refined the parting line to be as perpendicular to the positive surface as possible. After trimming and flattening the top, I added alignment dimples all around the part. I then trimmed the edges and glued the foam core sides onto the the box. I then added a bit of clay around the inside edge of the box to prevent silicon from seeping around the sides. A Picture showing the box and tools I used can be seen below.