The only bit that's stretched is the inner panel of the air intake on the left side of the car. Also you would have to consider the steepness of the parts next to the engine.
The MRT is small enough to fit into the whole file, so there is no generall stretching, except for the intake 5tag mentioned and the opposite side of the body, which is located on the actual side layer. Due to the shape there is stretching indeed. Sorry, i don't know why i did'nt look into it. It has nothing to do with personal preference - it was an accident :P
E: alright, here it is. MRT
As usualcertain parts, like the area around the engine and driver, need special treatment.
Yes, you could create your work at the 'stretched' size and then resize image back to the native skin resolution (square). However, some areas of the 3D model suffer more from stretching than others, so you might find these areas look a little strange in your final result.
Great resource! Glad this was a sticky. just started playing around with skinning on LFS, first skin I imported and my textures were out of shape...I found this thread minutes later.