re: Gas and temperature. Yes, it is true that gas that has been stored underground for a day or two will not change density very much when the sun heats the day.

However, if you pull in behind the tanker that has been baking the sun, the answer may be different. Additionally, you don't want to gas up directly after the tanker unloads no matter what the temperature. The filling of the underground tank stirs up any undesirables that have settled to the bottom of the tank and it takes some time for them to resettle.