I hate to have to second the motion, but the fact is that any antenna you
get will not do both jobs in a satisfactory manner. The wavelength of C.B.
and am/fm are not compatable. You will either get a good match on one or the
other, I would prefer the CB have the best match personally or you will burn
up the finals in your CB! (but I can fix that for you too!) ANY mount you
put on a vehicle is going to marr your finish, period. Whether it is a clamp
on or a mag. mount. If you try to "pad" a mag mount it will get a bad ground
and therefore "not match" again wrecking your CB.  (Yes I realize that mag.
mounts wont work on fiberglass) A gutter mount will indeed mess up the
finish too, you wont get a good ground unless you get into the bare metal .
There is  another option, but it requires drilling a hole in your Westies
roof. AAAAAAAAAHHHHHHHH!  Ok, calm down take deep breaths. Another way to do
this would be to mount a 102" whip on the rear bumper. (requires a hole too)
. The best placement for a cb antenna on any vehicle in center of mass.
(best reception and transmission) However,if it were me I would most likely
go with a gutter mount system. ( on a Westy) Anything else gets holes
drilled! I do have an OLD Cobra radio that has am/fm/cb all in one radio but
, it has a splitter and hooks up to 2 different antennas. Get a good "loaded
" gutter mount antenna , match it to your CB and then see what kind of
reception it gets for your am/fm, it may be acceptable to you, it just may
not "hold" stations as long thats all!   My .02 Tom