[Christ]

The exhaust heat exchanger idea, I've personally used in a golf kart. Air-cooled Kohler engine, and the pipe was just ingeniously run right behind the seat, dead center. It was quite easy to take some of the accessory power from the electrical system, cut holes in between the seats, and apply some sinks to the pipe, with a nice vent box around it that allowed external air to be heated at low velocity as it was sucked into the passenger compartment (enclosed, obviously). I wish I'd kept pics of it, but they're gone with most of my old half-finished projects.