What kind of vehicle, if it has a rear inside shelf I like the old UHF whip inside a tissue box for covert.
I know a bunch of guys who did exactly that in the old days. I'm following the thread because I bought a used P71 cheap and am "de-buffing" it (I
don't want to be driving around looking like what it used to be, so I'm changing the grille and tail lights to look like a Mercury). That's hard to do when you're a ham and need the antennas. I saw a guy who posted a multiband shark fin kind of antenna on Facebook, but then said the price was like $500. I'd just rather put a 5/8 over a 5/8 on the car before I'd sink that much into an antenna.
To Matt9638's point, what you might want to consider is finding burglar alarm tape and making an inverted T out of two strips, the bottom should be 12 inches, the top should be 6. Put it toward the back of the rear passenger side window (the one that doesn't open). Use the peel/stick screw terminals to connect your coax to the tape. You could also do an L shape, but that might be more directional. Or, you can put the shield right into the chassis of your Taco under the sidewall's plastic and upholstery and just have a 6" straight-up piece. Experiment around for what has the best VSWR. If the window has non-conductive window tinting film, you might not even see it from the outside.
I might do that with this car and try to make it look like part of the rear window defroster.
What I don't like are the AM/FM antennas with the coupler box. I had such a hard time with those in a past life. Going back a while, seems every time the deputy police chief keyed his microphone, his Syntor (not an X or X-9000) would gazorch the "local stereo station - you know, the one that plays that Frank Sinatra." The car had a fake cup holder that flipped up to conceal the control head. (As if people could not tell a fleet Caprice driven by a guy wearing a $20 off-the-rack Sears suit wasn't....)