Just remember that you're using the 12V after you hit the kill switch, so if you have the lights on and radio, etc . . . now you're pulling power out of that little lawn mower battery up front. And if I remember correctly you're losing the power steering (I could be wrong on that one, it's been a while)
And make sure you aren't pumping the brakes after killing it, you only get a pump or two before the brake pedal goes hard. One long slow braking action works best
Nice one on the 80 mpg tank, that's something I never pulled off in either of my Insights!