Ok, I just made a new one. Here's a step by strep of what I did (video doesn't show all of it)
1. Go to file>open ans navigate to ...\shapes\weapons\chaingun folder and open "chaingun.dds"
2. Import an image using file>open as layers...
3. re-size and place image as necessary
4. select "fuzzy select tool" in toolbox (with feather edges turned on and set to default 10, threshold set to 40 (may be different, so tinker with it))
5. select the outline of the cover on chaingun (make sure you have the chaingun.dds layer selected)
6. select the overlay image layer, copy, and paste as new layer.
7. Delete unnecessary layers then merge all layers.
8. go to file>save as and save as chaingun.dds
9. compression = DXT5
10. Save, your done!
Here's the video (opening steps and import of image skipped)