I think that the Trail has to be active in extending his/her off-ball range. When the T is off-ball, the T needs to extend his/her off-ball coverage to where the players are. This does not mean to take plays away from his/her partners but to be aware of what is happening off-ball and be ready to take care of business, when he/she has the best look at at an off-ball play.
I agree that the T cannot be standing around picking his nose and scratching his tuckus or scratching his nose and picking his tuckus, but needs to be active in off-ball officiating.