Can you guys give me a recommendation for climasheild XP for an underquilt ??

I just picked up 14 yards of 1oz ripstop from walmart for $1.50 per so I am good to go with fabric.

First off how wide and how long ?? I am guessing the width per hammock width ??
I am 6-3 - 235#.

I want a total rating of maybe 10-15dF. I will be packing a full length 3/8" blue pad. Not the walmart special, but one from bass pro shops. It is more dense foam.

Climasheild XP 2.5oz = .6", 3.7oz = .9", 5oz = 1.2"

The typical thinking as far as top quilts is that
2.5 is good to 45df, 3.7 good to 35dF, 5 good to 25dF according to Tim Marshall at BPL.

I plan to use the blue pad and quilt in combination for colder weather.

Thanks in advance.