These boxes “do what they say on the tin” and have become very popular among UK wargamers in the past few years. I have built up quite a collection of the things, mainly the 4 Litre versions which are a good size for storing 28mm models. Here’s one I use for my Saga Vikings.
For storing 15mm models I modify the boxes so that they can hold 2 layers of figures.
A frame built from 35mm x 10mm wood acts as a platform to hold up a tray made of cardboard and wood. The base of both box and tray can be lined with self-adhesive magnetic sheet, which will hold figures based on coins. I use British 2p coins or Eurocents, both of which are made from plated steel and get my magnetic sheet from Magnetic Displays/Coritani. They will sell you magnetic sheet pre-cut to fit the 4 Litre Really Useful Boxes, but I prefer to buy larger sheets, sized to fit box files, and cut them down myself. The price is the same and the offcuts come in handy.
Many of my 15mm and 1omm infantry are based on 30mm x 30mm bases, a standard size I picked up from Peter Pig rules but which I now use for all my WWII models. Command stands are 2p pieces.
I store these in Really Useful Boxes trays, each compartment of which will hold four of my standard bases – that’s a platoon for Battlegroup Panzergrenadier, or a section for I Ain’t Been Shot Mum.
You can fit two of these Hobby Trays in a 4 Litre box or four in a 9 Litre one. Or you can replace one tray layer with a wooden frame.