I Use GIMP for the paint versions it is free ware and works well for this. However I am having issues working with Campaign Cartographer I think it is too much a basic CAD. Can you recommend something else that would work and do the job in the simplest way possible. I know the thread is old but I really want to design a full space station and I want to do it in Tiles (Geomorphs).

Also I have some interest in creating some brushes for this purpose as well any recommendations?

Can you use the new Unity Mapping tools to create tile sets, is there a special way to do this and create modules?