"As far as hiding it, I'm not concerned about hiding the safe".
you really, really should be. If security is the bottom line. Safes have been cracked and wheeled off for many decades now.
I can build safes with 2" AR500 plate all day long, anchor them to concrete floors and walls with epoxy or wedge anchors. Put them in rediculously reinforced concrete rooms, but the biggest and best security for a firearm safe is unlocatability period.
Can't find it, can't steal it.
If you desire to show off your groovy full auto's to every girlfriend, then it's all on you.
Hide it and it's exponentially safer than out in plain view no matter what you build it out of. That's the plain truth.
Advertise it to every cute chic you meet, and eventually it'll attract unwanted attention.
I can breach or take, anybody's safe in short order with the common tools we use in our everyday work. And without creating unwanted attention.
Most folks have a safe to slow down a casual thief, a serious thief will be a whole nuther animal to deal with.
on edit, off site storage and a serious insurance policy is the only other option than being a target, iff'n you feel the need to show off your stuff.
Advertising very expensive items to the "babe of the week" makes you, and your home a serious target for theft and personal harm.