you can either hard code these values so that all packages will be calculated using the same dimensions, or you can add them to the cart on a product by product basis.
in your eCart object, create new columns for height, length and width.
In the Add to cart buttons, set the values for the height length and width, if you are using a recordset for your products, you will need to add theses columns to the DB as well and set the values in the DB.
in the shipping server behavior, you can then click the lightning bolt for the height, length and width, and select the corresponding cart column.
