I am working on drawing up a plan for my next project (when the thumb heals). I am going to build a built-in on a wall in my bonus room. Spacing is the tricky part because the sides of the ceiling slant down and there is a double window in the center. I want a cabinet/bookcase on one side of the window and a cabinet/gun case on the other. I just wonder if there is a rule of thumb to go by about how far apart to space the guns?