question in title lol
Mines an FH12, but basically the same.
I have mine under the radio in the Cubby hole, just make a hole in the back for the wires & splice them into the Radio.
Piece of ■■■■. 
PS: I could be talkin a load of bollox here. (wouldn’t be the first time) But I believe that some FH’s with the Factory fitted Ariel have the Coax terminating up behind the Tacho head, if so you might have to extend the cable.
so you power the cb off the stereo
how did you feed your aerial wire down into it
so it was all tidy …i think mie got factory fitted aerial because on pass side below locker there our to face plate pulled them off and there is aerial wire but with no connector and on the pass side on front of cab on roof there is a aerial but none of the others on fleet have got this aerial and it is in the place were all other lads with cbs there aerial is located in same place
how did you feed your aerial wire down into it
I didn’t mate, it was already done when I got me Waggon. I doubt it will be that hard though, just run it behind the trim on the A-Post & under the Dash.
It does sound like you have the Factory fitted Ariel, there not that bad really but dont expect any great distances.
Your only other option is a Mag-mount or stick one on a bracket on the back of the Cab & run the coax in through the cubbord.
The Sirio Hi Power 4000,is THE antenna to have,however it’s 7 foot in length,and is up there with the good old K40.
I had one when I last had a cb,before I became a licenced ham,and I had it on the back of my Premium,but because it was so tall,I had to put the mag mount half way down the back of the cab,with just the tip of the antenna peeping above the cab top spoiler,so it didn’t get damaged.
And if you need to put a mag mount on the back of the cab,make sure the point where the coax enters the magnet,points to the floor,to stop water dribbling into the magnet base,where the coax joins the stub.
And put some silicon on the point of entry,and also rub some around the part where the rubber gasket joins the magnet to stop water ingress.
Ken.