XFi, my garage used to be uninsulated like yours until I dropped a few bucks at Homer's. Glass insulation made a HUGE difference and was cheap and easy to install!
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Best tank ever: 72.1 mpg in February 2005, Seattle to S.F.
New personnal best 'all-city' tank June '08 ... 61.9 mpg!
Thanks to 'pulse-n-glide' technique.