Requirements
To import shipping rates the following fields are required:
This is the name of the shipping rate. The name must be unique and is used to determine if a shipping rate already exists or not.
shipment_logosSpecify one or more logos to show for the shipping rate. Multiple logos can be added by seperating them with a comma e.g. logo1.jpg,logo2.jpg. The logos must be placed in the folder images/stories/virtuemart/shipment.
countriesSpecify one or more countries the shipping rate applies to. Multiple countries can be added by seperating them with a comma e.g. Netherlands,Spain.
zip_startSpecify the zip range start.
zip_stopSpecify the zip range end.
weight_startSpecify the lowest weight.
weight_stopSpecify the highest weight.
weight_unitSpecify the weight unit.
nbproducts_startSpecify the minimum number of products.
nbproducts_stopSpecify the maximum number of products.
orderamount_startSpecify the minimum order amount.
orderamount_stopSpecify the maximum order amount.
costSpecify the shipment cost.
package_feeSpecify the package fee.
tax_id / taxtax_id: Specify the tax id of the tax rate you want to use
tax: Specify the name of the tax rate you want to use. The name can be found under Taxes & Calculation rules.
You cannot use both fields at the same time, choose between tax_id or tax
free_shipmentSpecify the minimum amount for free shipment.
The shipping plugin for which the field are going to be imported can be selected in the template or the field shipment_element can be used. The value to use for shipment_element can be found in the Joomla! plugin manager.

The name under Element is what is needed, in this case that is weight_countries. In your CSV file you can add the column:
shipment_element
weight_countries
Other good sources of information are: