2015 Cascadia Frustration

Hello all. I drive a company 2015 Cascadia. After a ton of research, I bought a Predator antenna, Cascadia mirror bracket, and coax from Bobs CB. Got it setup and using my Stryker 955's meter, it showed I had about a 1.1:1 across all 40 channels.
Along comes my GTM, saying I have to remove the antenna setup, that he was told it would damage the door.
So now I'm trying to get it working on the vertical metal grab rail mounted on the back of the sleeper. Running the coax from the Predator in the driver side window to the radio, I show a reading of 2.1:1 across all 40, raising the whip makes zero change.
Will switching to a 7' Firestik make any difference? I'm thinking there's no ground plane under that grab handle, so I'm screwed.
Sorry if I'm rambling, I'm seriously under caffeinated.

 

That's exactly the same antenna I have.
I even pointed out that I took both antenna and radio with me when I went home, so anyone using the truck while I was off could not damage anything. He said it would damage the door hinge and Freightliner would not cover it under warranty.
Funny thing is, I've been all over the Midwest and I've seen DOZENS of our company trucks with this exact setup.

 

Yep, I know I'm being lied to, but it's a company truck so until I get documentation from Freightliner, I have to play his game.

 

I was just running it in the window to test the swr on the relocated antenna, so the window was down. I had it run under the hood, through the firewall, inside the dash, to the dash top CB mounting plate...when I had my antenna on the door.

 

Yes, and he told me I couldn't do that either. It's the back of the cab or nothing.