For this particular game, I’m just making a landscape in blender and this is the setup.
My scene uses a couple of planes and the particle system to place the props on them.
For actual Skydome and using actual photographs, you could try this.
If you use the second link’s tutorial, keep in mind that you can replace the “Render the environment map” step with my Add-On.
Basically, once you get a scene you like to see from location 0,0,0 you can call my Add-On to get a 360° view to use in a Skybox.
EDIT:
A good way to make some without using a skydome and photographs, could be to setup some nice clouds by using the Blender’s cloud/smoke simulator.