It sounds like you are using the default Silex\Application class. The documentation isn't clear that you have to actually create a custom application that extends the default then initialize that. For example:
class CustomApplication extends Silex\Application {
use YourTrait;
}
$app = new CustomApplication();
Hope this helps. You can find more information on traits over at http://silex.sensiolabs.org/doc/usage.html#traits