Just an idea, I've been using a dip pen(not sure if thats the correct term)
Thats the only good picture I could find of one, sorry for it being so big. I got a generic one for like $1.50 at Hobby Lobby. It came with pigmented acrylic ink, black. The tip of the pen fits really well into panel lines. I've been using it off and on since last summer on my Gundams. I've had no problems with it. It took a little practice, but what technique for panel lines doesn't. It cleans up with water, if you make a mistake you can wipe it away. If theres a bit to much after it's dried, it sand away very easily. I've tried the Gundam markers and used different washes and paints. But for a straight black panel line, I've found nothing better.
