Well my experence has ben to do the panel lines after the gloss has dried. That way if you do make a mistake you can wipe it off easier and not ruin the paint if it smears. Also I had a bad experience with a marker and gloss! Im not sure if the marker was dry or not and sprayed on a coat of gloss and the damn line ran all the way down the car!!!
So be careful-and try to experiment with a old kit before doing it on a new kit.
Scott