I had a roo bar on our Vanagon which was great for 27mhz and the larger spring
mounted Flying doctor whip, On the I have fashioned 2 (27mhz and UHF) brackets
that attach to the outer top bolts for each headlight and protrude under the hood
, good earthing and good transmission reports although they are obviously
radiating towards the front.
An old fix for fibreglass roofs is to glue aluminum foil on the underside for the
required ground plane, useful for boats and fibreglass bodied ambulances.
