lol, I began sunning my diapers only about 3 weeks ago. All I did was hang the stained ones(didn't add a thing or even get them wet). After 3 days of success, here was my 4th attempt:

lol. The moral of the story is: it still worked! Turns out the snow was great for reflecting the sun back onto the diapers. Once the snow is gone I plan to put a white sheet under the drying rack. Though it should be noted that a lot of stains will disappear on their own after a few washes.
I also got gross sweat stains out of a white coat.