I know of situations where safes that have been bolted to the floor were still ripped out of the house. The best idea is to buy a cheap safe that can be removed. Add an old car battery or two for weight. Hide your firearms someplace within the structure of the building.
My neighbors house was broken into when I was a kid. Neighbor had a small, heavy safe bolted to the floor in a closet. Took the thieves all night to rip out the floor to get away with the empty safe.
I prefer to add ammo for weight. It's much more useful.