You can line it with Drywall for fire protection.

A good thing about the steel, locking storage box is that IF a gun is stolen and used inappropriately, you can show that you locked the guns up in "good faith". It also should comply with state regulations/laws. One thing I would suggest is one of the heavy gauge steel safes that will come apart to move. Maybe not as good a a welded safe, but probably better than a thin gauge steel box! Anyway, good luck, hope you never find out it can be forced open!