25400 - Illegal to carry a concealable firearm. http://law.onecle.com/california/penal/25400.html
25610 - Exempts transportation in a vehicles locked trunk or locked container. http://law.onecle.com/california/penal/25610.html
Other exemptions appear in the statute citations;
25450, 25510, 25515, 25520, 25525, 25530, 25535, 25540, 25545, 25555, 25560, 25565, 25570, 25575, 25580, 25585, 25590, 25595, 25600, 25605, 25610, 25615, 25620, 25625, 25630, 25635, 25640, and 25645 (for the sake of brevity I will rely on your due diligence to read through and familiarize yourself with the statutes. I am also reminded of a quote from Tacitus- The more numerous the laws, the more corrupt the state.)
Some will also warn that 25505 limits transportation between to destinations with reasonable deviations. i would point out, that it is legally unclear if 25505 is attached to all or just some of the exemptions of 25400 - Im sure that this wasnt intended to include peace officers, for instance.
The short answer to your question is that it is viable if you are willing to accept some margin of legal risk and take the responsibility to know what your rights are and invoke them.
Specifically, since you are transporting a firearm in a locked case - no one will see it and therefore it is not subject to search under the 'plain view' doctrine. And without a warrant you cannot be compelled to unlock your private property for the police to conduct a search. And if somehow police do break the lock or otherwise open your container and discover that your container has in it an unloaded firearm, the burden of proof is upon the state to prove that you were NOT transporting it directly to or from 'any motor vehicle' or any destination which is specified by the numerous exemptions provided in statute. Volunteering any information to the contrary would be devastating to your legal defense.