Pretty much automatically here a buried tank is called for which are normally at least 25-30 ft from the house. Commonly 500 gal.
We have problems getting propane companies to install and maintain tanks for generators. Unlike propane used for heating and cooking, generator propane never gets used. Propane companies make their money selling propane which covers the cost of providing the tank and maintaining it. If all you have is a tank that needs to be topped off maybe once a year, there's no money in that especially with an expensive buried tank and the installation.
And we have a lot of paranoid quasi-rich people here that have hissey fits when, God forbid, their power goes out for an hour once every 5 years. They MUST have a generator!
-Hal