Cuda Fastback Cargo Area Carpet Underlayment

Looking for some input on what the factory placed under the cargo area carpet on the flat floor section. Was it a hardboard material similar to the spare tire cover in the trunk area? Was the carpet glued or just laid down on this piece? My floor panel had indoor/outdoor carpet glued directly to the sheet metal panel. I 'd like to do it correctly with the new carpet. Any comments and pics would be greatly appreciated.