I have been hammocking with my Big Agnes bag which has a pocket for my Thermarest pad under me--no down on the underside. It's been great but last weekend I felt on the edge of cold. I'd estimate the overnight low at around 40. I am thinking of trying an underquilt but I can't afford to spend a lot. I have found a Grand Trunk down blanket for under $100. Think it'll make a decent DIY underquilt? It'll be full length and packs small/light but I'm not sure it'll be warm enough?