As long as you understand what you see in the UV map template you can bring that template up in  Photoshop and start adding layers to your UV template and painting over it. For instance, let’s say you have UV mapped your freighter using box coordinates. Your template will show the back, front, left and right sides of your freighter so when you layer over the template you can paint over those UV guides. You can then add another layer over your painted layer using a grunge texture and using the overlay mode for that layer and adjust opacity accordingly. Then save as bmp, jpg or whatever format you intend to use giving it a different name. When using that model just call up that saved image as its texture map.