With small hand held plasma cutters and battery powered cutting tools nothing is theft proof anymore. A safe or locked cabinet well stop most smash and grabbers as they well only spend minutes in your house. A pro that knows what you have, knows when you are gone and well take any and all of what he is after.
I converted a walk in closet for my collection. Added solid core door and three dead bolt locks. It well only slow someone down, not stop them.
I think a monitored alarm system is a better investment than a high dollar gun safe.