Here are a few tips that I can offer-
2. Don't limit yourself to just painting on the surface of your fused plastic- try painting on canvas or fabric and the cut out shapes or strips of your painted material and sew it directly onto the surface of the fused plastic.
1. Use silkscreen ink in place of paint. I have had the most success with no FLAKING and will typically paint my first layer and then painting on top of it with either acrylic paint or even paint with the silkscreen ink. Speedball makes a great affordable ink in a lovely variety of colors.
3. Try the opposite- cut up your fused plastic and use strips and shapes to sew onto canvas or fabric.
5. Paint the surface of the fused plastic and fuse another clear piece of plastic over the top.