MUST ground the shields that's OK and you can use lightning arrestors
on both coaxes.

This is probably not going to work in most cases. Remember an open wire
feedline can have
rather high voltages on it compared to a matched coax liine. This is
because they are often
mismatched at the antenna.
If a voltage peak should happen to occur at the place where you have the
arrestor, it can fire
the gas tube because of the rf voltage.
For example, a gas tube arrestor made for legal limit typically has a firing
voltage of about 800 volts. In a matched
50 ohm system, even with a full 1500 watts into 50 ohms the peak rf voltage
is in the neighborhood of
600 volts. But even a moderate power into a high impedance open line could
be enough to fire
the gas tubes. Neither the transmitter nor the gas tube would be happy with
this situation.

Rick K2XT