For some upcoming cold weather hangs, I need to upgrade my stock Hennessey's insulation capabilities. I've grown strong in the ways of DIY, so I am ready to undertake the next level of do-it-yourselfery. That said, I'm a tad unsure of how to approach this project.

I haven't yet decided if I want to modify the Hennessey for this, since a new hammock is in the works, as well. Regardless, I'll be using an underquilt and a top quilt (as opposed to sleeping bag). This seems the lightest/smallest way to accomplish my goal of a warm nights' sleep.

Based on a given fill material (down, let's say), insulation rating is basically dependant upon thickness, right? For temperatures down to 10 degrees, and a wind-sheltering tarp, can the minimum down/insulation thickness for my needs be calculated, or is there more to it?

I've seen a couple different methods for attaching underquilts; everything from bungee cord suspension, to velcro, buttons, and even magnets. Is one significantly better (more durable, lighter, more reliable) than the others? And the top quilts I've seen folks make appear to simply sit atop the occupant; are they in fact secured in some way?

The design I envision is a fitted quilt attached to the outside of the hammock by buttons every foot or so in a grid, all the way up the sides to the edge of the netting. On the inside, a top quilt is attached in some way at the edge of the netting as well, overlapping with the outer quilt. Velcro or something would allow me to open the top quilt enough to lean forward and step out of the velcro fly, and through a tensioned slit in the underquilt. Is similar to what other people have done, or am I just over complicating things (or over simplifying them )?