I'd like to setup a large tent on my property for storage. We get lots of sun and it gets hot. Winters are generally mild. No snow, some rain (25-40 cm a year). I can get old army tents pretty cheaply but how to I make them last?

Arizona has this famous tent city jail that they operated for years using old army tents. How did they keep the canvas from disintegrating in their harsh sun? What other things should I be concerned with when trying to keep a tent in good shape?