I have a 30" two-way antenna mounted in the center of the roof, there's just some places it won't fit. Had to take it off while on vacation this year, getting to our parking spot in the condo required driving through the garage under the whole building to get outside to the parking area. Serious pain in the ass, had maybe 2" of clearance, and would have hit the sprinkler heads in the garage, which would be expensive. I carry a rain cap for the antenna mount. I also have a mount for an HF antenna in the bed, those antennas are anywhere from 6' to 10' tall when mounted and tuned.
No magic antennas, they need to be a certain length or they don't work. There are ways to shorten them, but it's always a compromise.
The "stealth" antennas on police cars are for 800 MHz, the antenna only needs to be a couple inches long anyway. They do make them for lower frequencies, but they're complete ****. And expensive ****, at that.
I use my FM radio constantly, been thinking of getting a better antenna, since the station I listen to doesn't come in for a good 20 minutes of my commute.