MKMT,
I have to disagree with your statement that EVERY car on the streets has a rear window defogger. There a still a few of us true sports car enthusiast that think that a sports car, or a muscle car, should not have such things as rear window defoggers, automatic transmissions, power windows, power locks, air conditioning, etc., etc. Such things should be reserved for the handicapped, the elderly, the lazy, and those who think of an automobile as something you RIDE in, and not something to be DRIVEN.
So, if you are modeling a Corvette it should not need a rear window defogger as a Corvette is supposed to be a sports car. If you are modeling a Lexis, then it should have a rear window defogger just like any other good "grocery getter" driven by a soccor mom! It is a sad commentary that with all the SUVs on the streets that the only off-road experience the drivers have is in a golf cart! Food for thought.
If you are going to add the rear window defogger be sure to hang a scale handicapped sign on the rear view mirror for scale accuracy.