I painted a lexan driver figure with Posca pens, it needed more than one coat and is vulnerable if rubbed, ever with a finger as it comes off, however once sealed with lacquer (Halfords UK) it was ok. Not sure how even the coverage would be if you did a whole car body.
I have to pay a premium for Tamiya paint as Im offshore and normal mail wont deliver, so I have to pay for a different service, but its worth it for paint that works