Do you get errors opening the storage box in the demo? The red and green chests are both examples of a storage box.
You can look at those events for examples on how to setup storage boxes.
In text, it's something like this:
potion = [0, 1, 4]
spear = [1, 3, 1]
shield = [2, 1, 1]
items = [potion, spear, shield]
open_storage (0, items, "Red Chest", 79)
But you have to make sure that none of the lines go over the limit and onto a new line.
The best way to do it is to not use such long names like potion, spear, etc... and instead use something like this:
a = [0, 1, 4]
b = [1, 3, 1]
c = [2, 1, 1]
items = [a,b,c]
name = "Red Chest"
open_storage (0, items, name, 79)