Very hard to explain, as ive been doing this for a long time but....ill try an explanation....
1-Download the WDB Texture extractor found here http://trucksimsforum.proboards.com/...play&thread=14
2- Go into the Rig'N'Roll/Trucks/Trucks/Freedom (As an example)
3- Make a backup of the Hercules_Freedom_res
4-Drag the Hercules_Freedom_Res and wdb extractor to a new folder (XXX)
5- Drag the res file onto the wdb extractor
6- A new folder will be created.
7-Choose the skin you wish to edit and open it with your editing program
8-When finished editing drag the edited skin into the wdb extractor, this will auto repack the skin into the res file for you.
9-Drag the Herucles_Freedom_Res back into the rignroll/trucks/trucks/Freedom
10-Start game
11-Choose the skin you edited
12-Drive around
13-Have fun...
14-Obey the rules of the road
15-Enough directions? xD