I bought a sheet of 1/8 thick foam from Mcmaster Carr.. One layer in the bottom, the second layer had the cut outs. A little spray adhesive to sandwich them.
I don't have the case any more, but I think I still have some of the foam.. Not sure if there is enough, but it wasn't expensive.
When I sold the case to a big time collector he told me it was the best repair job he had seen. If that means anything