I have an Icomm mobile that is useless to me because it is too easy to fumble the multiple knobs and buttons when underway even as passenger and change a dramatic setting. I could dedicate it as my shack 2/70 but I prefer my Yeasu 8900
Refresh us on the antenna model. You may be able to adjust the antenna itself, but none of those other ideas are likely to make the SWR better, you are already pretty good
It all depends on how robust your local mesh is. In areas with dense mesh, it definitely is viable reliable alternate to the common infrastructure you are completely dependent on. Just because you don't participate does make it weak.
RoadApple is correct. All you need to know for your application is LMR-400 or equivalent, short length, but even more important HEIGHT.
You are correct, you need your antenna higher than the surrounding metal radio frequency Faraday cage barricades. In the VHF & UHF ranges the saying is: HEIGHT IS MIGHT.