There is a rule about this, we just use the word “vehicle” in it, but it also includes mortar etc.: “No Excessive Un-Cap Vehicle Camping (AA sitting in base for more than 5 minutes)”
Probably should make the rule more specific, but you are in your right to be mad at this player for mortaring.
Since origin and starting BF4 don’t work as of right now, maybe NOW could be the time….Though there are players still. But thanks for the reply. Appreciated.