Ok.
Once and for all, in the spirit of malicious compliance:
Dig a basement for a new house. Pour a vault room while they're doing the foundation walls. 18" reinforced concrete walls, floor and ceiling.
Before the ceiling is poured, site build a container occupying 100% of the volume of the vault using steel beams and steel plate walls. A steel box inside a concrete box. Have the blueprints clearly depict that the steel box "could" be lifted out and flown away, if you had a star ship and a tractor beam. It's definitely a container. Now secure the box within the vault using interlocking pins, super adhesives, whatever you can think of to make the box a permanent part of that vault. Pour the ceiling. Build the rest of the house, steel and concrete, above.
Install a bank vault door, time lock, multi part biometric locks, the whole deal, like on those spy movies. Obviously, will need hvac inside along with lighting, etc.
Now, inside, rack up all pistols and rifles. Put a trigger or cable lock each, so you're compliant with MA law.
Center of the room, setup a pedestal, with a clear acrylic box over it, ring the pedestal with a matrix of lasers and LED lighting, maybe even an info plaque and a security system warning sticker and inside that case put some crappy old, half rusted H&R six shooter.
I mean, you're going to jail anyway, so you might as well have fun.
/satire
Yes, I know. Humor in a law thread, but the OP question is long since answered to the extent that it can be.
Whatever happened to that guy in Lowell who had a vault darned near as secure as this one I described, some guys broke in and spent a day drilling into it and made off with some guns?