Question about Skinning?

Please excuse me if I have Posted this in the incorrect board/thread but I have a question about skinning. I am currently making a skin for the 2015 Formula Reiza championship. I have made skins before but not on open wheel cars. I have painted the file named SIDE, however you can only veiw the right hand side of the car. I noted that the default decals placed on the templete had two sets. One was placed normally and the other was inverted, like looking through a mirror. So my question is how do I place decals that they will appear on the left and on the right of the car with the correct orientations and inverted correctly etc?
Thanks in advance Guys!
p.s I'm using GIMP

The guys to ask are Christo and Gary.
Riaan is also a top class painter.
If you can pm me your cell number, we can add you to the ShadowracingRSA group on whatsapp. That way, you can get hold of them easier.