I have the Cobra 75 with a 4ft firestick, mounted with the arizona rocky road mount.
The CB is mounted under the steering wheel:
it is grounded in the red circle, I added a nut and bolt and it is very nicely grounded.
I then have the coax wire ran through under the center console, then under my floormats, under the back seats then under the plastic in the rear out through the hinge hole for the rear gate and back into the rear gate.
Then out and up to the antenna mount by Arizona Rocky Road.
I have a quick disconnect and a spring connected to it. I leave it on most of the time but when I go into a parking garage or a drive thru I can jump out and remove it quickly. Also when I go out to sea for a short period of time I take it off and put it inside.
Here is where I have the wire from the box to the handheld.
I took it to a local Ham radio/CB shop and he said all of my SWR signals are really good. I have held conversation in local San Diego with guys 5 to 8 miles away approx.
Hope this helps.