I found a good way using a modeler and a fairly easy image manipulation.
Basically you need a good 2D program such as PS,a sky texture or photo.
prepare the image:
Take your sky texture(or photo),add a little linear gradient in the bottom of your picture just enough to get some kind of horizon foggy-line...Now with Photoshop6 select FILTER>DISTORT>Polar Coordinates...In the setting choose RECTANGULAR TO POLAR.The filter shouldn't distort the clouds too much unless ALOT of detail was involved(and eventhough it's not THAT bad) and it should have deformed the gradient to a circular one by now.
MAake the sky:
This is the easiest part...Make a sphere,cut it in half to make a dome,select all of the bottom vertice and scale them just a little bit to be able to select them appropriately in the UNWRAPPING process.
Now apply a planar mapping on the TOP of the object and you should edit just a few vertice to finnish it.No seams.