If you question is about the art of the skill ^^, then I would not choose a rocket. A Rocket does not fit any class (Maybe only engineer), and certainly not the Warclaw. Siege weapons are also more ancient nature.My suggestion would be a lasso or something similar, a chain? Maybe with different skins and effects (definitly only playable in WvW), maybe defending on the server color. If there must/should be a mastery, then a quest on Borderlands not often used places (Scrits on NW Alpine Borders and so on).