Not a lot of talk about DIY down underquilts. Seems to be mostly topquilt work. I'm headed toward a down UQ. A couple of questions.

I have rectangle UQs(synthetic) that I'm happy with and contour to the hammock fine. Is rectangle OK for down too? I've never seen a "commercial" one, so I don't have a lot to go on. If I've missed a thread on down underquilt construction, feel free to point me in that direction.

Second question: I'm in Georgia so 99% of my winter hanging will be 20-50 degrees. How thick should I make it to have a little bit of insurance against slightly lower. I'm thinking 3.5" with a little overstuff, but I'm also thinking that's possibly overkill. I don't want to invest the time/effort/money in down and not make it warm enough. I'd rather have it a little overkill than a little overkill.

Thanks.

Jbo