user exit st location

Hi,

The requirement is to have storage location populated in sales order. I know that it can be done using USEREXIT_MOVE_FIELD_TO_VBAP and writing a code to pull the LGORT value from TVKOL table.

But how to go about doing this ? Do I need to create an enhancement or directly write the code in the userexit? Could someone plz brief the step by step process ?

thanks in advance