Five minutes on Google has convinced me that temp and humidity are critical, but tuning doesn't seem to be an issue.
If tuning were critical to storage I would think it would be mentioned here:
Piano Storage
I should point I that I don't own a piano, don't play piano, and don't know a damn thing about pianos.
Oh, but yes, you're cheap. Just get it tuned. It would be great for your son or some other pianist to give you an impromptu concert and have it actually sound good.