Wow, this was a pain. If John wasn't there to help me I'm sure I'd have walked away for a week, frustrated. Laying the foam into the form was definitely a pain, and getting it all to fit nicely was very tedious. We ended up spending a lot of time fussing with drywall screws, trying to hold the foam into the form correctly. To make matters worse, I didn't have time to do the layup by the time everything was set up, so I left it overnight. By morning, the dabs of 5-min I had used to hold the foam down had let go, and I had to spend another evening repairing them! If I had to do this step again, I would definitely adjust a few things:
1. Install more slats. The plans setup is just barely acceptable, and raising the height 1.5" put me over the edge support-wise. I would recommend installing at least 2 additional slats per side, and packing them more closely as you go up the curve. It doesn't take long to install them, and it's cheap insurance.
2. Make sure the flashing is installed VERY firmly at every spot, especially at the top where the curve is most complex. I had used a roll of aluminum tape John had lying around, and while this was great at first it didn't stick very well, so it gave way at the top and allowed the foam to buckle.
3. Don't put your joints at the ends. You want them even so you don't get a noticeable line on one side, but that doesn't mean they have to be at the lip. Instead, cut each foam strip in half in its middle and add the extension piece there. There's not much flex in that section, so you don't have stress on the joint. If you're careful to use very little glue, you won't get a joint line (it's easily sanded, anyway).
4. Use twice as many foam strips. It sounds time consuming, but if I had used 3" strips instead of 6" strips, they would be easier to shape for a good fit and install. Make sure to install extra flashing, of course, but I think this extra setup effort is well worth the result.
Re Turtleback Bulkhead...My turtleback doesn't have a bulkhead because it has a spar inside it where the bulkhead would normally be. See pictures and comments above and below.