I wish my son only weighed a quarter pound, especially near the end of a trip and he only wants to ride on my shoulders. It makes me especially grateful that I cut my base weight to 8 pounds.
Thus far, i've had the bivy out on three 3-day trips in Western North Carolina in night time temps ranging from 70's to mid 30's. I have noticed that in warmer temps, the inside of the Momentum50 has gotten clammy, but never really wet. I also notice that the bivy definitely adds some warmth to my old down sleeping bag. I think the mesh face panel has helped with condensation. I do use it under a tarp when I am expecting some sort of precipitation. I use the bivy as mostly piece of mind under an open ended tarp instead of an uber light weight shelter. Another factor that may have reduced condensation issues is that I haven't sealed any of the seams since I am relying on the tarp to deflect the bulk of rainy weather.
I think the silnylon was a good choice as it is fairly durable and water resistant. I haven't made use of a ground cover since I have been taking the bivy sack and the silnylon has held up well.
In total, I think I spent 3-4 hours max making this bivy sack. Not too bad considering it was my second go at some MYOG.
My first was my tarp that I posted on here