Confirming that this works. Summary: Export private key: gpg --homedir /.snap/gnupg/ --export-secret-keys -a This will ask for passcode used to create key. Key is dumped.
At destination machine, create privkey.txt with above contents gpg --homedir /.snap/gnupg/ --import ./privkey.txt This will ask for passcode. Key in same passcode.
snapcraft keys - Output now should contain the imported key