We lost the rear compartment cover from our '64 Safari a couple of years ago and were able to make a very good replacement. We purchased trim (aluminum extrusions) and the correct aluminum sheet material from Vintage Trailer Supply. Pre-69 trailers used 2024T Alclad, I'm not sure what was used from '69 onward, but someone here does. Our cover replacement cost about $100 in materials and maybe 90 minutes to fabricate.
The fabrication was very straight-forward. I added side slide locking bars for extra security to the new cover. It originally had only the lock.
Let us know if you need some photos or more details.
Roy and Marie