Our '83
Casita 13 was licensed in Michigan when we bought it from a couple in Bend, Oregon. The Michigan plate was eternal, so they had hung onto it.
Could not find any VIN anywhere; the Casita factory folk said it was originally an adhesive sticker placed on the side of the frame up near the tongue and good luck finding that after all these years.
Took the trailer and Michigan
title to the Springfield DMV, where they inspected the trailer to verify the absence of the original VIN sticker, and then issued an assigned Oregon VIN for the trailer. It took 20 minutes to get the trailer re-licensed and they handed me the new plate at the end.
The very helpful DMV lady was emphatic that trailer theft is very common and we should have the new Oregon VIN welded onto the frame in two places, as well as keep the trailer locked up at all times.
We also bought an original VIN sticker from Casita, but it has no legal standing in Oregon, it's just a vintage item at this point.