Going to install a Kenwood mobile GMRS in my '18 F350 (aluminum) and 1/4 wave antenna. I have a back-rack/headache rack on the truck that has a slot for accessories and I have a mounting plate to go with it (also aluminum). The mounting plate is 8" square. I would drill the plate for an NMO mount. It would make a clean installation but I'm wondering if that's a good enough ground plane or will performance be a lot better if I mount the antenna directly to the roof?
Obviously, a magnetic mount won't work on an aluminum roof so would have to drill into the roof, which is not a big deal, but prefer not.
Is the ground plane only the surface the antenna is grounded to and not surfaces around it (like the roof)? Would the width of the backrack (same as truck bed width) contribute to the ground plane?