If you want better performance you should start with a whip, make sure it
is tuned
(using an swr meter) and well grounded to the car.  Ground the radio to the
chassis too.
   As to where to mount it, the theoretically best spot is in the middle of
the roof,  and
I too think the westy top couldn't take it unless it were metal.  The
bumper is a grand
place mechanically and works well,  but it'll perform  better if you can
get the base
if it higher.   I saw  a photo of one mounted part way up the rear
hatch.  The owner
bolted a plate bent to  fit the door jam to his bus and  mounted the
antenna there.   I
have tried mine on  my yakima  roof rack that is bolted into the  shell -
only bumped
*some* of the overhead wires.
Clearly too tall.

Adam wrote:

<snip>
 > HI all, I'm looking to install a CB in my 91 Westy and wonder if anyone
 > has tried using the adapter that JC Whitney sells to allow you to use
 > your existing antenna as both a CB and regular AM/FM antenna. I would
 > like to not drill a hole in my roof but I need decent CB range up here in
 > Alaska.
<snip>

diverse_imaging@yahoonixthespam wrote:

Drilling through the roof of your Westy is to be avoided at all costs.
Doesn't make for a good ground plane (read zero), and it'll introduce a
source of leakage and weakness.