My '18 Highlander Hybrid generates S-9+ noise on the HF frequencies whenever the car is 'on' whether it running on the gas engine or the electric or just parked.
I have decided to go with a separate LiFePO4 battery for power and operate only when parked. Unfortunately, that means not being able to run the heat or AC, so mobile operation is a 'nice weather' affair, parked, for me.
Take along an all-band portable radio and try it in the car you are considering. Of course extensive bonding and ferrite use will probably also be necessary, but see what the car sounds like with the all band portable will give you an idea of what you may be up against. I am surprised no one else has responded; I guess most mobile ops are using internal combustion engines.