STEP 4: SEAL THE INTERIOR
Apply glue to the inside of the hollow, and if any of the pages have become separated during the hollowing out process, to the outside page edges as well. Weight and allow to dry.
Repeat step 4 again, trimming any scraps and tidying up the corners as necessary. N.B. For the second round, the outside edges were all firmly glued together, so I left the book open in the sunshine to dry.