Pianting the stripes is actually far easier than using the kit decals, I used the kit decals on my Typhoon
article here and it was a pain, although it looks pretty good. getting the decals in the right place and on straight is the hardest part.
When painting on the stripes paint the white areas first, let dry. Mark off the positions of the black stripes, using a pair of dividers, lay thin strips of tape (Tamiya masking tape is the best for this) to these marks. The Mk 1 eyeball is remarkably accurate for getting these things straight. I lay the tape on one mark, near the wing leading edge, pull slightly taught, eyeball it straight and lay it down over the marke near the trailing edge. You can either carry on around the underside of the wing, or mask seperately. Just be aware of the overlap. Fill in the area of white to be masked, I use cheaper masking tape for this.
Note:
Always use the cut the edge of the tape at the masking edge. Even if you are going to use the full width of tape, cut the masking edge, use a steel ruler and a sharp knife. This will ensure that you have a clean edge to mask with. Also the thinner the tape the easier it will conform to compound curves.
Scale stripe width: Invasion stripes were 18" wide on fighters that works out to 0.38" or 9.53mm (say 9.5)
Bombers were 24" (I think) that works out to 0.5" or 12.7mm.
HTH
Mal