I have downloaded the Hex stackable storage boxes from Creative Electronics - https://makerworld.com/en/models/62733?from=search#profileId-144869. I had them stacked 6 high and 3 wide but they would move on me when opening and closing drawers so I made the connectors to hold all of them together and it makes it much more sturdy.

Be gentle when installing as its easy to crack the hex pattern on the box.