My Hennessy Expedition is zip entry, so I probably have less trouble than you will. I use a CCF pad, 5.88 from WM. I cut it in half and use it as a torso pads, two laid side by side, overlapped so about 30" wide, and laced with a couple of mason line cords to keep in place. Such would work well I thinkj, in a bottom entry. I used the torso pad down to 40 deg with no problems, so it should work well in summer temperatures. Absolutely no need to spend a fortune on an underwuilt. The short pad works well from an insulation POV, and I don't find it in any way uncomfortable, so see no need to spend money I don;t have anyway on an UQ..