As an aside, I remember as a kid being puzzled why a car that was being flat-towed by an RV had smoke coming out the tail pipe. It wasn't until years later I realized the owner had very likely left it in gear, and was back-driving the engine to probably about 8000 rpm...
Separate story: I flat-towed my mid-engine car which uses a FWD drivetrain and even though it was in neutral, the transmission housing was fairly warm at the end of a 20-mile tow.
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Midlana book: Build this mid-engine Locost!,
http://www.midlana.com/Kimini book: Designing mid-engine cars using FWD drivetrains,
http://www.kimini.com/book_info/