The major issue with corrosion proofing is that the key areas such as joints never had it.
The airframes were usually painted after assembly with zinc chromate.
For it to have really worked would have required zinc chromating all the panels and airframe components prior to assembly.
Cars in that era were built to last no more than a decade at best. Piper and Cessna aircraft are still flying after half a century. That is good going by any standard.