I think I have finally solved the nasty post shut off gas smell when storing my 1st Gen van in a garage. I ran across an ad for racing fuel deodorizer from Jegs and Summit Racing. I'll admit I was skeptical, but I spent the $15 or so shipped and tried a bottle. It actually works! I premixed an ounce into a gallon of gas and then poured it into the tank. It works as stated, exhaust now has a slight sweet flavored smell to it, I bought the Raspberry but it comes in 10+ flavors. After shut off, a sweet raspberry odor, kinda like a scented candle is all that remains in the garage. It lingers around for a few days but no more gas odor, amazing. There seems to be no difference in performance of the engine either, heck they claim they use this in dragsters running nitro to get rid of that nasty odor. Worth a try if you are having the gas boil smell.
http://www.jegs.com/i/Power+Plus/290/00041/10002/-1
http://www.jegs.com/i/Power+Plus/290/00041/10002/-1