Chris from Man Made DIY put this unique secret compartment together. He cuts out a large portion of some old 12″ vinyl record covers. he then glues them together using some pine boards for reinforcement. The build process is documented here.
The finished result blends right in with the existing record collection. This same process can duplicated with hollow books or other CD and DVD cases, but application with records looks pretty good and has more interior volume than any other versions we’ve seen.