Divinycell will not hold a screw at all! I used it for my coffin cover and had to over drill all the holes and fill with thickened epoxy. If not done this way the only grip for the screws will be in the skin. I lammed one layer of mat onto the skin just to even it up and then bedded the foam into the epoxy. Last layer was one wet out piece of 1708. Even today after two years no issues. The whole thing now acts like a diving board with just a little flex. If you are bridging a wider area I would highly recommend 2 layers of 1708 on the bottom for more stiffness.
Plywood weighs around 40 lbs per cubic foot. Obviously the Divinycell you are looking at weighs 5 per cubic foot. Coosa 26 weighs 26 and so forth. Quite a weight savings on a large area! Good luck!
