I mounted my ladder rods within a tube and made a physical connection at the top to hold them in place. worked excellently.
The other trick i learned was to make a third electrodes at the base, which is connected to a side by some HV Mohm resistors.
This makes it easier to start the arc reliably. Made it ideal for a museum display we made
http://i139.photobucket.com/albums/q295/JHowson/Jacobs%20Ladder/IMAG0111s.jpg
Here are some slow motion shots we took of it starting using this electrode
http://i139.photobucket.com/albums/q295/JHowson/Jacobs%20Ladder/Ignition/ignitionslowmo.gif