I built the duct jig next to plans and mounted it on a table for easy access and rotation. The first layer of 10mm foam was cut and strapped to the jig. As seen on the photo, straps blocks of wood and a little heat gun rounded the corners near the cutout. They tended to want stay flat. I then swapped out the heavy straps for thin packing tape and glassed over the top of them. The second layer of 50mm XPS foam was the cut and the bevels were chopped out with a hotwire. They were then slit 40mm through for bending around the jig. At this point I had a major brain fade (senior moment)and put this layer on inside out. The next morning I realized my mistake and had to fill all the slots with QCells. Not happy with myself. Anyhow the next outer layer of 50mm XPS was cut , bevelled and put on the right way. So much better. I also ran a twin core cable between the layers from the top of the duct to the cutout in case I wanted to put a light on top. The duct has come out very strong and perfectly round. I now have to set up some mounting plates and rudder bars etc before the final outer and inner glass coats.
Ouch on the first layer of XPS. Are the instructions too vague? Do they need clarification or improvement?