You cou;d just clean them and then store them. No need at all to store them with sani in them, or water. If you want to be particularly anal clean, sani and purge them with co2.
That's what I do. I clean them and once they're dry I put enough CO2 on them to seal them. I sanitize right before I use them. If they aren't pressurized when I go to use them, I know I have a leaky keg.