I've been investigating the underquilt world for the past 2 months in preparation for creating one for my Hennessy ULBA.
The designs have been narrowed down to a basic Klinsky model. I've made a few changes to the model, and I want to run it by everyone here. Please tell me what you think.

Grosgrain trim - I like this better than a simple hem, both aesthetically and functionally.
Lack of large diagonal elastic - Klinsky put a large elastic diagonal from one side tie out, underneath, and then to the other side tie out. I think it can be eliminated without any performance loss.
Shock Cord vs. Elastic - rather than elastic being installed around the perimeter of the quilt, I envisioned shock cord running through the grosgrain and out to tie outs on the hammock support line. This would allow me to have better control over the space between the hammock and underquilt and the ability to replace the shockcord if needed over time. I was thinking about two long pieces - one for each long side - and two short pieces - one for the head and foot.

Other information: I'll be harvesting the down from an old blanket, so while it will not be 800+ down, I'm using what I have, and I expect to use most all of it. I'm not sure actually how much down I have to work with so this part should be an adventure all by itself. (Thinking about the tent set up in the living room... LOL) I'm using 1.1oz DWR ripstop for the shells and I haven't given much thought to the actual suspension at this point. I can figure that out later. I expect the entire project to be about 16-18oz or so.

Any thoughts about the modifications? Is the shock cord as good of an idea as I think it is - or not?
I always forget and make it more complicated than it needs to be...it's just walking.