Incremental Shipping Rates Based on Number of Items

I want to use the zones shipping module but it does not seem to have the flexibility I need.

I want to charge the following shipping rates:

UK and Western Europe
$15-00 for the first item plus $10.00 for each additional item

South Africa
$15-00 for the first item plus $5.00 for each additional item

Asia
$15-00 for the first item plus $10.00 for each additional item

How could this be achieved please?

Sometimes the easiest answer is to stop looking for the "free" solution.

For any shipping that isn't immediately covered by the ZenCart default options, I would strongly recommend Ceon's Advanced Shipper module

You can easily "spend" a lot more than the cost of the module in using your own time trying to manipulate the ZC defaults.

Please note that I make no personal gain should you decide to buy this module.

You could clone the Item Rate item shipping module and build 3 Zone Definitions for who can use which module ...

UK and Western Europe
$15-00 for the first item plus $10.00 for each additional item
Use the settings for:
Handling: 5.00
Rate: 10.00

South Africa
$15-00 for the first item plus $5.00 for each additional item
Use the settings for:
Handling: 10.00
Rate: 5.00

Asia
$15-00 for the first item plus $10.00 for each additional item
Use the settings for:
Handling: 5.00
Rate: 10.00

Do a search on:
clone item
clone flat

do see how a shipping module can be cloned ...