When propane generators were in style many rigs had larger LP tanks to supply them with fuel. If you don't have a propane genset, there usually isn't a need for a huge tank. The exception, of course, is winter heating for those who stay in the frozen lands.
You can add a tee to your system that will accept a feed from an external tank - it's called an Extend-A-Stay from Marshal Brass. That way you can hook up any size tank the local LP sypplu place will deliver to your site.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL