2 Meter / 440 question.

I have an RV with a fiberglass roof and a luggage rack on top of the
roof. I'd like to use the luggage rack as an antenna mount point since
there's really no other place to attach a mobile antenna if it needs a
ground plane.

But I doubt if the rack is grounded to the vehicle frame. Should I
bother running some ground braid down to the frame or will the coaxes
shield itself provide enough ground to allow normal antenna
performance.

Thanks.

Dave