I drive my G maybe once every 2 weeks or so. Gas isn't going to go bad after 1 week, or 1 month. I try to keep it round 1/4 or 1/2 and then fill it up every other time I drive it just to keep some fresh gas in there. No issues... ever.

If the gas is "evaporating" out, there is a bigger issue. With all the smog equipment on the car everything having to do with gas is pretty mch sealed up tight. I assume you are parking it in the garage... do you smell gas?