Something like this,
It's not much, but it was the biggest that I could get into an upstairs bedroom. It comes with lagbolts to anchor it to the floor and wall studs. I shoutld probably move mine to inside one of the closets,
Beware, though, that its not the least bit fireproof.
I knew someone who had a heavy safe out in his garage, but this being in the so-called "rust belt", I didn't want my firearms in the garage.