having hard time getting good match for cb, wonder if is bad ground on antenna, aluminum body?

 

If ground is a problem it will not be caused by the aluminum body. However, paints, these days, have a lot of polymer in it that can act as an electrical insulator. Make sure you are grounding to metal.

 

SWR is affected by a great number of things. Testing in a garage or other enclosed space, testing next to a building, especially a metal sided building to testing near power lines to an improper PL259 connections to the coax. Check the coax for continuity and look for any signs of breaks.
As KW said, the aluminum body should have nothing to do it. I've put lots of VHF / Marine and Police Radio's as well as CB's in fiberglass boats. Not much grounding with fiberglass....

Test with a dummy load on the radio and see what the SWR is. It should be perfect. You can put a PL259 on the antennae end of the cable then put your SWR meter there and check the SWR. Then connect the antennae. If that is where the bad SWR starts showing up, check everything there is on the antennae.