Introducing the new FedEx multibox shipping plugin for VirtueMart 2. This is one of the more accurate FedEx shipping modules as it breaks the user's cart down into packages based on FedEx's limitations and specified configurations on how products should be packaged.
This plugin will assume that all products can be packaged together up to the point of maxing FedEx's limits (based on length/girth and/or weight). Once those limits have been met for a package, the plugin create a new package. Those packages are then sent to FedEx for a rate based on the sum of fees for all included packages.
You can, however, force that products be packaged alone or define length, width, height, and weight exceptions that tells the plugin what can be packaged together and what cannot. For example, let's say you have a product that is 25lbs that is 12x10x8 inches. Using the defined custom fields, you can define weight and dimension exceptions to package other products along with this. Let's say you set a weight exception of 50lbs and a length, widght, and height exceptions each set to 25 inches. The plugin will then package other products with this one until it reaches a maximum of 50lbs or a combined length, width or height of 25 inches. Once the exception weight or dimensions has been maxed, a new package is created.
If you have label creation enabled, the plugin will have FedEx create labels as either PDF or PNG files for the packages the plugin created. The plugin will display what products (including quantity) it packaged together, the tracking number, and a link to the label (saved locally to a specified folder) for each package it generated. That way you can package the products similarly in reality.
Read more about it here