You can change the size of a teleporter in its properties under Collision. There is a value for the radius and the height. Rightclick the bar over a viewport and chose Actor -> Radii View. This will make the size of a teleporter (or trigger. Works the same for triggers) show up as a red cage.
Some properties can be triggered. E.g. PainCausing. To do that just trigger them by giving them a Tag and have it match a Trigger's Event.
I think triggering volumes only works with PhysicsVolume and its subclasses.
Edit: Check out KF-Offices-story for the "gas volume" I made there.