Thanks for the info and photo! I like it-- very simple and easy to deploy (and clone). I built a model last night, with an idea to sewing the under cover in place, but I am leaning to Velcro, especially for prototyping. I'm still thinking about baggy box-shaped under cover that covers all but the last foot or so of each end. Kind of like taking the Clark pockets idea and replacing them all with one continuous compartment. I'm thinking very seriously of adding Velcro to my Hennessy Zip and making insulation modules for that, borrowing from the Garlington Insulator concept. With Velcro it would be easy to ventilate the pocket too.
Differential cuts are mandatory to avoid compressing the insulation. With the Speer version, the issue with air gaps is eliminated all the way around and it does leave the opportunity for different quilts to be mounted. It would be easy to make a partial quilt with light fabric ends or just a lighter quilt overall. You could insert a vapor barrier/space blanket, Insultex liner, and so-on. Some have written that the UQ needs to be tight against the user, but I think that is more an issue with air gaps on a shock-cord mounted UQ, where you get gaps on the ends and air leaks down the unfixed sides.
The idea for a Velcro bug screen had occurred to me. I would have Velcro on the outside of the underquilt, so you could attach the screen to the quilt, or to the hammock body without the quilt in hot weather.