To set up a Custom Box/packaging in Ordercup, that you can then select for a Package Type when in the shipping screen:

1) Go to the Settings Tab

2) Click Custom Package Type on left menu panel.

3) Click on New Custom Box button

4) Name your Box and fill in the proper dimensions. You can also optionally specify a weight for the box, if you want to have this weight added to the weight of the order fetched from your cart. If not, please leave it as 0.0.

5) Click the Save button and you are done. 

You can now select this Custom box from the Package Type drop down from the Ship tab, under the Custom boxes list.