ABHiker: Sounds like your #4 is working but you need to hold the pads together. Have somebody make a light Cuben envelope to hold them together. Once you have the envelope you can try different combos inside it. For years I used a 1" layer of open cell urethane on top of a thermarest. In general I've given up on the very light thermarests due to slow leaks that are impossible to find in winter. I suppose the envelope could be refined so that there are just cuben caps that fit over the pad ends and are connected with cuben stringers. I believe there is such a thing as going lighter than a person needs to. Not getting good sleep to keep arbitrary base weights low is something I don't do.