Good day 708!
Please have a look at the Midland MXTA26 antenna and the NMO mount. I have it on the center of my roof on my Tuscon. It has 6 meters of coax- please do not shorten it. This antenna is tuned to GMRS and I am using a Midland MXT500 mobile radio. Whether on my car or on a steel sheet in my back yard, I am hitting my local repeater that's 14 miles away- (houses, trees, the moon, etc. are all in the way) and my SWR is less than 1.2:1 across the board. Transmitting and receiving beautifully!
All the best!
Dan
WSBV762
https://midlandusa.com/products/micromobile-mxta26-6db-gain-whip-antenna
https://midlandusa.com/products/mxta12-antenna-mag-mount?_pos=2&_psq=mount&_ss=e&_v=1.0