Any chance the Ping would work inside a balsa/fiberglass hull if it was bonded tight against the inside surface?
Well after reading that even painting it is not a good idea I doubt bonding it inside a hull would be a good idea
I have made several standard sonar transducer installations inside small boats.
With fiberglass hulls up to 20mm thick.
Works to ~150 meters depth.
Must be no air inside the hull at mounting position.
Test can be done with a waterfilled plastic bag, put the bag between transducer and hull to test location.