Looking on youtube, I saw a SOL 2 person DIY underquilt solution. It would definitely meet my needs. 1) ultralight, 2)compacts very small, 3) provides a wind and rain barrier and 4) very cheap.
I usually sleep warm and have slept to 40 degrees w/o an underquilt. I just need something that will help with an extra 10 degrees should temperatures drop (like this year; hit 27 with high winds). My biggest worry with this solution would be moisture. I would use shock cord instead of paracord.
I only use a hammock when I go on hiking trips, otherwise I use a tent. So, it will get about 5 nights a year in use. Interested in your comments. Link

I am not sure, but worth checking out, doe's the space age material used to make those survival blankets breath at all. could it be a condensation problem?

quote bwcasolo: "I am not sure, but worth checking out, doe's the space age material used to make those survival blankets breath at all. could it be a condensation problem? "

Mylar does not breathe. It is a thin plastic sheet that has an even thinner layer of aluminum deposited on both sides of the plastic. It is a perfect vapor barrier.

I think I will give it a try. Total cost will be under $20 and it will give me a small project. If I do get condensation, I can always fold it up and use it as an emergency blanket again.

Let me know how it goes. I saw that video also and was interested.