Hi David,
I usually makes panel lines on aircraft using mixture of water, dishwashing soap, and chalk pastel. I scrap the chalk pastel using modeling knive or cutter, put the chalk powder in a small cup, pour water and a small amount of dishwashing soap in it then stir it. after that, paint the mixture to the model along the panel lines. wait for a while until it dry completely. after it dry, wipe the model's surface with damp tissue paper. don't make itu too wet because it would remove all the 'paint' of chalk mixture on it, just wipe it on the area inside the panel lines. you may do this process over and over again until you feel satisfy with the result. the panel lines filled with the mixture makes it stands out over the panel area surface, creating a great looking panel lines.
I used to try using pencil, but the tip of the pencil was not small enough to create a good panel lines.
okay, happy modeling, my friend!
<donny>