Check it out
. The controls are pretty self-explanatory. Set the resolution and other parameters as needed. Enter some random alphanumeric characters for the Seed and hit enter, or just click on "Randomize Seed." Once you have a space skybox (a 'spacebox,' you might say) that you like, then right-click on the generated image in the upper left and save it to your computer. Then open the image in your image editor and slice it into six pieces, export those to .pcx, and import into your .utx file. Voila: spacebox!