I have decided to stop using a pad while hanging, but I don't want to invest in an expensive underquilt as I never camp in areas cold enough or windy enough at the time of year I go to need something that expensive. I was looking through stuff I already have and I have a sleeping bag liner and a bunch of down. If I sew the liner closed and put a draw string or something on one side so I can open it and add/replace down as needed, do you think this would work or not worth the time and effort?

should work, check out the diy underquilt postings, scroll down a bit. also what was key for me to stay warm was an underquilt cover for 35$ from 2qzq. just google that. 2qzq is the company, couple from out east, they do great work with sewing on hammocks and hammock gear.

quote ChasenRahl: " If I sew the liner closed and put a draw string or something on one side so I can open it and add/replace down as needed, do you think this would work or not worth the time and effort?"

You'll want to baffle it as well, otherwise the down will migrate into a pool below you, and keep your shoulders cold. Having just bought a JacksRBetter Winter Nest, I can see why they are expensive - not only are they baffled, but the baffling is done by sewing no-see-um netting IN BETWEEN the fabric layers - no through stitches. That's well beyond my DIY skills...