What we used to do (and this was on the old AM sets, and it worked for me on the new? FM sets) is use a piece of telly arial cable, or satellite, as the live feed from the batts to the Squark box, the inner core wire was wired up to the live feed from the batt, and the outer braided bit was used as the earth feed, the outer braided bit shielded the live wire from a lot of exterior electrical interference.
I used the same thing when i was on the waggons, ERF's were notorious for electrical static, plastic cabs you see. 10-4?
Now depending where you mount your antenna, depends your transmission area, middle of the roof equates to all round transmission, like a circle, now slightly to the rear means most of your transmission will be thrown forward, like an oval facing forward, likewise mounted slightly to the front, means most of power will be facing rearward. Clear as mud yet?? #-o.
