Hi, you need to create an alpha channel that tells the paint to be tougher against damage. If you create a black alpha channel it should pretty much not wear at all. (there will still be dirt but not scratches.) this only works on the custom paint job style, styles like patina only allow you to edit particular parts of a weapon. If you join my group I am working on a few tutorials that might help...
http://psteamcommunity.yuanyoumao.com/groups/Coridium

added a tutorial about this to my workshop guide... http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=297595853