Hi Wurger, the pencil line method is done before the gloss is applied, it is quick and simple and as Adler said not messy, you just need to be careful, if you slip you can easily gouge into the adjacent panel , then you need to lightly sand back to plastic and respray. If the slip is light then a clean rubber removes the excess lead line. You must keep the sharp point to get into the panel line so you only do a bit at a time.
Here are two more shots, now showing the gloss applied and ready to apply the decals.