The only thing that blocked that opening was a vinyl "curtain". On earlier cars you should see about 4 snap fasteners, or their remains, on that little shelf where the sheet metal goes over the rear axle. On later cars it just hung down. This was fastened to the body underneath the trunk hinge panel, there were two alloy strips running through a channel in the top of the fabric and was pop riveted to the body. The early style vinyl used tended to go brittle and come off. The later type was more robust and tended to last. The one on my early car was nothing more than a small strip up under the trunk hinges when I got it.