If you want an automatic load door (like used in caves), then filter "Auto" in doors and it'll pop up.
If you want a trigger to open a non-load door, you'll need to script it. You could either do some conditionals on a trigger event, or just make the trigger stretch over both sides of the door, and use the OnTriggerEnter and OnTriggerLeave events to open/close the gate (either through activation using the default triggers you've described, or PlayGamebryoAnimation).