I have been shutting the fuel off at the sediment bowl.
(24 touring car) If not, I noticed the same thing, 1/4 tank when parked, no spots or stains on the floor, no gas smell (and I looked in on it periodically).
Come spring...tank dry.
I did find, to help seal the cap, an oil filter gasket for an Import (don't remember what), fits on the cap and helps with evaporation and I don't smell gas when driving as much. Gas won't eat the oil filter O-rings.