I have been experimenting because I have the exact same questions. I made two frames and covered them with Ultracote. I drew some panel lines on them with a Sharpie then sprayed one with Testors Dullcote and the other with Krylon Clear Satin. Unfortunately both coatings made the Sharpie lines blur slightly. The Dullcote was worse than the Krylon but that may have been because it was a little heavier coat. The good news is that I was able to shrink them with an iron afterwards. I'm thinking of trying some other things for the panel lines such as pastels or a grease pencil.