Antenna issues

Try this mount.
HD Volvo Freightliner Kenworth Peterbilt STAINLESS STEEL CB Antenna Mount | eBay

 

I was running the same radio,box stock, through the stock antennas on a 2016 VNL sleeper truck and it actually worked really well for me. I am pretty sure the stock Volvo antenna system only uses the driver's side for CB and the passenger side for AM/FM radio. Just pop another stock antenna on it, check SWR's and run it! No need to reinvent the wheel if you're just looking for decent results from a stock 4 watt CB.
Now if you want to upgrade your radio to something bigger, that's a whole 'nother story!

JD

 

The door offers best performance with no effort for lowest cost. Mounting elsewhere will result in worse performance or higher cost and more effort to achieve the same performance.

 

Run the cable and install the connector(s) later

 

You can use either the mount that @rabbiporkchop suggested or the bird perch that I use that screws into the oem mirror mount. Just remove mirror mount screw and screw the bird perch in. Driver's side only!!!! Using a screw in bird perch on the passenger side? It will loosen up going down the road.
Volvo Bird Perch Antenna Mount BPM1
Route your coax down along the door and into the engine compartment and there should be a grommet covering a hole that will feed into behind the dash down low.
Takes a bit of fiddling but you should be able to get the coax up to your radio from there.
The door should be fairly well grounded to the cab and if not, a couple of braided ground straps on the hinges from door to cab should fix that up.
I, myself wouldn't bother with a coil antenna for your setup. A bit harder to tune in my experience. Just use a good fiberglass, top loaded antenna with a tuneable tip such as Firestick 2, Skipshooter, etc. Keep it under 5 foot to miss the trees!
Ground plane.......I'm not an expert......the whole truck would be your ground plane. The better your antenna system is grounded to the truck, the better your radio will operate. Mr porkchop can explain it better.

Good luck!
JD

 

This coax can make life a little easier for installation.
Wilson 305-830 Super Mini-8 Coax Cable with Removable Connector
Not the best coax in the world, by any means, but will work and make installation easier! Readily available in any truck stop.

JD

 

I drive a 2017 VNL, bird purch drivers side. You need to use 18 foot cable. Run the cable under the door frame molding. The across the top of the windshield with cable clips you can get at most truck stops. Cones in a 4 or 5 pack. Run the cable to the center of the windshield then up into the cubby hole for the CB. I use a 4 foot firestick adjustable tip antenna. I swing 80watts on my 665 Stryker radio, and maintain a 1.0 swr . I do tilt the antenna forward some.