Roger,
The best way to paint the camo is using round foam tape and a spray gun. You can get the tape from auto paint stores. It's used to mask door jambs on cars. The beauty of the tape is two fold. First it has an adhesive already on it. Second it gives the right edge along the camo.
So you draw in pencil the camo outline on the wing and fuse. Then you put the tape along the pencil line and affix it down.
Then you paint the area. It's a pretty straight forward process and not difficult.
Once finished remove the tape and admire your work!
Don't forget to get a good reference of the Camo patterns. They aren't wildly nilly but pretty specific.
The original planes were painted using large masks and were pretty standard from plane to plane.