Hi there Dickie,
I’m interested to hear how you got on? Did you resolve the issue? I’ve recently finished another camper install, and found the ONLY way to get the SWR down was to use a top-loaded antenna with the top-loaded section completely above the roofline, and 2/3 of the remainder above the ‘fibreglass line’. About 4 inches of the bottom of the whip is close to the steel-body, but unfortunately that was unavoidable.
Motorhome/Caravan CB Radio advice and troubleshooting