AS Joe said the easiest way is to make a full side psd. The process I use is:
Create a new psd, I usually just start with 4096x2048 dimensions.
Open an existing texture from the plane that already has stripes and copy and paste the individual sections on to the new psd lining up all stripes and parts of the plane. Line them up so that it looks exactly like the plane in the sim.
I then open the blank textures and copy and paste using the same method. Use the opacity slider on the blank textures so that you can match them exactly with the previous textures. After you get the full side done you can just paint on this and copy and paste to the individual texture sheets.
I hope you can understand as I don't think I explained it very well.
Here is a pic of the Carenado 185 full side that I use to do all my paints.