a pair of these
https://www.tractorsupply.com/tsc/product/stack-on-18-gun-beveled-edge-safe-gcm-1918-dxthey aren't fire protection and they aren't going to keep a person with knowledge and tools out , but if kids/grandkids and criminals with out tools are what your looking to keep out.
if you need a 10 gun you probably need a 20+ gun because they are like tents the manufacture stacks then in like sardines to get that number
you can always start with one and see if it is enough room
remember to secure it to the wall and floor with screws/lags and big fender washers
if you can put it in a closet or build a closet around it that can offer some fire protection, as well as making it more difficult to get to the sides and such with pry tools.