Lunar Secure Case: has a storage slot of 1 x 2, you obtain this on the start of the game.
Mars Secure Case: has a storage slot of 2 x 3 that can be crafted at a Workbench Level 2 with 1 Lunar Secure Case, 5 Toolbox, 500,000 Luna; or it can be bought at the Heidi's store for 5,200,000 Luna with a Trading Center Level 2.
Venus Secure Case: has a storage slot of 2 x 4 that can be only bought at the Heidi's store for 8,800,000 Luna with a Trading Center Level 4.
Saturn Secure Case: has a storage slot of 3 x 3 that can be only bought at the Heidi's store for 25,600,000 Luna with a Trading Center Level 7.
Jupiter Secure Case: has a storage slot of 3 x 4 that can be only bought at the Heidi's store for 51,200,000 Luna with a Trading Center Level 9.