"Rollie" wrote in message
...
I thought it sounded like a good setup, but I checked the internet and
found
the URL below. Maybe it would help to spread a few ground wires out from
the base of the antenna to be sure of the counterpoise effect. I have an
SUV with one of the antennas in the middle of the roof. When talking to
local operators they tell me they can see the difference in signal when
the
vehicle is pointed away or toward them. Must be a good counterpoise off
the
roof.....

http://en.allexperts.com/q/Ham-Radio...-Roofing-1.htm

For frequencies below 50 Mhz. you can't get enough counterpoise. Yes it
does matter which way you are facing because you probably can't get decent
symmetry below 144 Mhz either. Center of the roof helps but you will be
operating at rest, a bumper mount will at least do better somewhere. I have
a metal roof and it does change the loading from the typical ground mount,
but is an improvement. For a while I operated from the shack with 40' of RG
8 out to the truck with Hamsticks.