In article ,
W5DXP wrote:

Don't forget the Arrow Open Stub J-pole.

http://www.arrowantennas.com/osj/j-pole.html

There is (or was) a nice writeup of this variety on Cebik's web
site. He refers to it as a "variant J-pole". The feed arrangement is
different (it's open at the feedpoint, rather than being fed a few
inches above a short), and the arm lengths are different than with a
"classic" J-pole. The current distributions are different, of course,
but the radiation pattern is only very slightly different than the
"classic" variety.

I have one of these dual-band types in my "go-kit" (it's actually a
knock-off, built locally based on the plans that Arrow used to have on
their web site) and it's served me well. I usually mount it at the
top of a two-or-three-segment aluminum mast, sitting in an old hefty
movie-camera tripod base.

Much too large and heavy for a vehicle, of course, but I imagine you
could build a somewhat-similar open-stub J-pole using much lighter
materials (e.g. fiberglass whips with wire fastened inside or
outside).