Some interesting responses you have received. I think however something
important has been missed.

On HF frequencies the received signal level is unimportant. What is
important is the "largest difference" possible between the signal level
and the noise level. In many cases improving an antenna tends to
increase both noise and signal received by equal amounts amounts. (I
should point out that this improvement does help transmitting though as
at the other end you become a stronger signal relative to noise) A
ground improvement in your case may reduce some losses but wont affect
the S/N.

So ask yourself what you would do to increase the S/N ratio. A directive
antenna may help, reducing local noise (like from generators etc) will
too. I would guess that given you are mobile your options are limited.
There have also been suggestions already about other antenna systems to
try. If however RX S/N is the most important to you I would try a
magloop for receive and a dipole or 1/4 wave GP for transmit!

Cheers Bob VK2YQA

OZUser wrote:
As an avid 4WD SUV owner I do a lot of outback travelling (Austrlian
Deserts, Cape York, Kimberly Coast) and as such have a Barrett 950 HFradio
&Barrett 910 Autotune antenna installed for comms.

Would it be preferable when camped / stationary to earth the vehile to a
"ground" ground = what I am looking for is a better receive signal ?????