CA PC 12026.1 (c) answers your question. There is no "list of approved containers". The requirements are specific:
The law was not written to prevent theft. It was to prevent law abiding citizens from accessing their firearms whilst transporting/possessing them.Code:(c) As used in this section, "locked container" means a secure container which is fully enclosed and locked by a padlock, key lock, combination lock, or similar locking device.