Did Travel Trailers have VIN's in 1972, boats didn't require HIN's until the mid 70's. I had a boat built in the early 70's and it had a serial number, but it was just a few numbers. Possibly a trailer that old didn't have a long VIN number like they do now, possibly just few numbers stamped into the frame somewhere.
2014 F 250 Gasser
2019 Outdoors RV 21RD
"one life, don't blow it", Kona Brewing
"If people concentrated on the really important things in life there'd be a shortage of fishing poles" Doug Larson