I saved on the underquilt by going with Snugpack, which makes a huge difference for hammock ass when the overnight lows drop. The Blackbird has an integrated layer underneath for a sleeping pad, but I prefer to just use the Jungle Blanket because I don't like the added stiffness of a pad.
I purchased a couple of SnugPak Underblankets to use with a Hennessy and a Warbonnet Blackbird. The picture on Amazon makes it look like a fleece blanket...it's not. Check out the customer pictures to get a better feel for it. I haven't taken this down to the 30's, but the lower 40's were just fine. You do have to dial in the suspension a bit, but that's half the fun. :)