Underground fluid storage tanks with substantially higher capacities.
Mods introducing new content into the game.
More than just chests.
When I manually pick up a 5×5, 400k storage tank, it is placed in my invetory as a 6×6, 576k storage tank.
This is also a problem for me - makes it harder to move tank locations without losing materials and the added pain of the 6x6 inventory growing over time