It was somewhere outside Barstow when Mike Halmarack
wrote:

But for immediate use do you think it would
provide a waterproof glue of a similar quality to Cascamite?

No, nothing like that dependable quality.

It'll work (although for home-made glue, IMHE rabbit-skin is easier).
As a demonstration for kids it's excellent, as a piece of woodworking
recreation it also has its place - Italian renaissance furniture,
AFAIR. But I wouldn't trust it for boatbuilding !

The problem is with acid production owing to decomposition in service.
As the Germans found in WW2, this is a big problem.

The German "Moskito" aircraft was a copy of the British Mosquito,
likewise made by a bonded plywood process. When built with the
original "Tegofilm" adhesive, a hot-melt sheet (aliphatic PVA ?) it
was a fine aircraft. But the REAF bombed the Tegofilm factory and so
an ersatz glue had to be found. Now AIUI, this was a casein glue. It
was soon found that the Moskito developed a tendency to break up in
flight, caused by glueline failures. It wasn't the glue that was
failing, it was acid byproducts of the decomposing glue weakening the
adjacent timber. The aircraft was abandoned.

If you make it, you have to watch for development of acid afterwards.
Given the amount of flour that some people dilute Cascamite with,
without evident trouble, you may well be able to bulk up your casein
glue with chalk whiting and buffer any acidity as it develops.