Opencart already has the payment gateway included.
But when customers click to pay they are refered to Skrill Moneybookers site and after payment they return back.
WITH THIS MODULE CUSTOMERS WILL NOT LEAVE YOUR SITE ANYMORE.
They will pay directly from your site without refering to the skrill moneybookers site.
There are 2 extension: for opencart 1.5.x and opencart 2.0.x
It works with all themes, no overrides, simple to install and use.