Bambi II (smallest trailer the year before your '65 Caravel
was produced) had an original Dometic RM45. We got it running thanks to the assistance of a local Amish LP appliance repair shop. It worked for 1.5 years and then died, presumably due to a hydrogen, not ammonia, leak. This according to the same LP shop. I searched and asked...it is NOT rebuildable.
We replaced with a Norcold N305R. It is close to original size/specs, but a bit smaller. Exhaustive research found nothing closer, though we would have liked a more direct replacement. A bit of cabinet modification and it looks like it has been there for 50 years.
After install, it looks and works just fine. We ordered from the biggest vintage trailer parts store online and received two badly damaged units. We had to send both back...and lost a month of trailering with a refrigerator. Finally, we canceled the order and bought directly from a local RV parts/repair place who deals with COMPETENT shippers. One and done. And $10 cheaper than the online giant. Sometimes if pays to shop local.