My Steel Box

Picture not that well staged...but have just got this box from Freecycle, and was thinking of making it into a water feature after taking off the lid.  But now have cold feet on this - as it is a bit bigger than I wanted to do at the moment, so thinking maybe I could use for storage in the garden, but assume I need to do something to stop it from rusting really quickly?

...I guess this would have been a problem with the water feature too!