For people, who like to store rifles in drawers, this will be a good fit. I am thinking about swapping mine as they are too high and are wasting space.
3 l will do for most rifles, 5 l for launchers and helmets etc. The are stackable. Only problem might be to source them, when you are not living inside the UK:
Really useful box: Desktop organiser 3/5 litre Really Useful Drawer
Here the specifications: