If you are using conventional radials or counterpoises for your antenna then an earth rod at a lightning arrestor on the antenna side will be OK.
The additional gas discharge tube and 1 M ohm resistor on the new version of the HF Antenna Isolator is intended for use with counterpoises isolated from ground. I wrote an article for the RSGB RadCom magazine showing how to reduce RF noise from local sources using a vertical antenna with isolated counterpoises.
