CaliRaised Cb antenna mount high swr

Hey all, i recently got my hands on a new CB setup. I'm using the caliraised antenna mount (driver side) and my antenna is a 4 ft wilson fiberglass. 18 foot of firestik brand coax to a cobra 25 LTD my issue is i cant get my SWR to tune down below about 3.4. Anyone running this mount experience issues with high swr? i have a feeling it could be related to the composite beds on our trucks. but the ground wire off the cable is connected to the metal by where the tail light mounts. any thoughts? I'm going to look at it again tonight after i get off of work

 

Ground to the chassis or metal fenders larger surface area metal. I actually mounted to the front of the truck because I could not get good SWR in the back probably due to the composite bed. I even tried a no ground plane antenna setup for a while and gave up moving to the front of the truck with a hood channel mount and quick release antenna setup. I now have good SWR. More metal surface area in the front.

 

I'm either going to try moving ground to the area behind the headlight or straight to frame. Read another thread from a guy that mounted an antenna to a tool box and ran into the same issue.

 

Yeah the tool box in bed won't be a good ground either. See how the chassis ground works? I didn't try it as I decided to use the hood mount instead.