While reading your entire blog over a weeks period, I saw someone mention the Espar heater and how it heated air, but if you look at
Espar - Coolant Heaters you will find that they have one to heat water. So, heat water for your heater core, and also heat your batteries during the winter. Use the Diesel one and run it on WVO to save even more. You could also run some tubing under the seat to warm the backside too.
Ed ... hoping to talk the wife into letting me build one of these.