I have a 120 mounted in the center of the roof
of my Chev Astro Van. I believe our roof areas
are roughly similar.
5w phone, I've made contacts all over N America
while mobile from Phoenix. Canada, East Coast, Mexico,
Pac NWest, all while mobile on 5 watts, 40 and 20m.
Simple hole mounted, ran with RG58.
Make sure it's grounded well at the base
of the antenna (scrape, sand etc the paint
where the PL259 mounts).
You'll know it's not grounded well enough if
the screwdriver function doesn't seem to work.
Craig 'Lumpy' Lemkewww.n0eq.com