SimHQMotorsports uploaded a nice custom skin tutorial for use in the ISI rFactor 2 beta.
This video shows how to add .dds custom car skins to rFactor 2 (Build 218).
Shown is the SCES v2 rfmod which includes the LMP1 and GT2 cars. More details on the SimHQ Motorsports 2013 SCES endurance racing series is here.
Tutorial by http://www.simhqmotorsports.com/