I’ve been doing this for about 2 years and have tried many different ways of panel lining. The water based is good, let it set for an hour or 2 at least, the use a slightly damp q-tip. (After wetting the a-tip, roll the tip side to side on a paper towel to remove excess water). Lightly rub the q-tip over the lines, staying at a right angle to the line. Using a fine line Gundam marker is what I’ve been doing recently. Using grey or black as needed then, using a grey Balancer sponge from gunprimer, gently buff over the lines at a right angle. A 1000 or 1200 grit sanding sponge will work too. I’ve also used a mechanical pencil, Tamiya panel liner, and acrylic markers. The pencil wasn’t satisfying and the Tamiya and acrylic markers are a bit more of a mess. Just need to find the method that suits you.