I did the same. Bought our 500 gal underground when I got tired of renting an above ground from the propane company.....that let me shop companies. Then I added two more 500gal above ground tanks off Craig's list. One was couple years old, $800 ( they ran natural gas where the guy lived and he didn't need it anymore ), and the other was free.....just come get it. I repainted both, had the gas company plumb them into my existing line, and install two new primary regulators ( first one was gone from the tank, the second one was too old to trust ), so now we have 1500gal storage. I keep the second two full and shut off, just as backups. We'll use 300gal or so per year out of the underground.