I sanded after each application of fiber and resin. I put on 2 layers of carbon fiber and 2 layers of regular glass fiber. Also applied some resin thickened with micro balloons and glass fibers to use as a mud and help smooth it off and make it flat.
Finally it was ready to open and see how I did. I had to push a putty knife between the layers of plastic tape and the targa strip to help release it. But it released fine.