I like this option, you could build this for a couple hundred dollars. face the weapons towards the rear seats making a false wall, when you need access, lower the rear seat backs. Also change out the stock seat locks with another locking solution, so that the rear seat backs have some level of security, or optionally, completely remove the locks on the seats and place this on a rear hinge that would lower down for access from the trunk to the weapons, then make your locking system accessible from the trunk area (locks securing the false wall), so if someone breaches the trunk they don't see the weapons in a quick search. If you want it really secure, have someone fabricate the exterior with 14 gauge steel shell or even aluminum (or call
80/20.net and have them fab something for you once have have the dimension) and hinge with locks, then cover it in automotive carpet, if you are not skilled at this go see some car stereo shop, they can easily build this, just have them sign NDA's, so the don't run their mouth or post it on their website.
I thought a little more about this, you may want do build it under the trunk carpet, where there is already a tub, you have to keep your trunk clean for quick access.. then you would only need one piece of 14 gauge steel, a hinge and a lock, you could line the tub with a trash bag (for easy removal) and spray foam the whole tub, then do your cuts outs for our weapons and gear. then follow the directions above... would be a lot easier then making a whole false wall, and would be more secure with quick access from the rear trunk. Optionally you could use the trunk, but it's definitely not as secure, if you do the front, it might be easier, I would add an
Powerlift for the Frunk if you go that route, for quick access.
Model 3 power liftgate
Frunk auto opening and easy close kit
You may not get a full size shotgun in there, but a
Kel Tec KSG bullpup will fit, or a collapsing stock AR along with mags, flashbangs, or whatever cops carry today for criminals (pacifiers, get out of jail free cards, etc). You could also run 12 volt power there to keep a backup battery for your communications gear, tasers, light etc.
Another option