this is the reason truckers run co-phased antenna's. The truck body's are fiberglass.
The Jeep also has a less than optimal ground plane but it gets the job done. I'm gonna co-phase 2 102" whips just for fun.
'06 TJ X Blue w/dark khaki top, 4.0L, 6 spd, 3.73, 30x9.5R15 Wrangler GS-As mounted on Ravine wheels, Soft-top w/half doors, 4 100w ProComp Offroad lights(2 bumper, 2 windshied), Cobra 29 LTD w/4' Firestik, Custom rear storage box.