To reiterate what another comment said : The sky you choose should match the overall light on the ground! If you had “white-cotton” skies, then there were probably no shadows on the ground – and if you drop a bright blue sky full of fluffy clouds (or worse, a sunset) behind this, those with a more critical eye will notice the two different qualities of light. However, a “textured gray sky” that looks a little gloomy and stormy may match the ground light much better – and can even add to the mood of the shot.

Here’s the result of my first attempt. While the sky in this shot was not technically “blown-out”, it was just a pure, featureless white that looked blown-out. The cold-looking clouds came from a hi-res public domain file I found with Google Image search.

Thank you!

Shame really, because the rest is excellent. I just cannot figure how to “Paint on the mask in black” or “remove these using the Burn tool”. I’ve got the settings, but nothing’s happening. So I’m off to try somewhere else instead.