Suitable for 18L, 35L, 50L, 64L and 84L really useful boxes:

-18L Really Useful Boxes can hold 2 trays.

-35L Really Useful Boxes can hold 3 trays.

-50L Really Useful Boxes can hold 4 trays.

-64L Really Useful Boxes can hold 6 trays.

-84L Really Useful Boxes can hold 8 trays.