You could gtt the Hennessy under shelter system which is designed to work specifically with a bottm entry HH. I assume that the UK HH distributor stocks them. I think this is a bit pricey and use a CCF pad system, adapted to a bottom entry Hennessy. Take one blue pad, 72"x20". It is too narrow to protect hips and shoulders, and the length is difficut to manage in a BE HH. I made a wide torso pad by cutting the pad in half (36x20) lay the pieces side-by-side, overlapped to give a width of about 32-35 inches. Punch a couple of holes in the overapped parts and lace a couple of lengths of mason line through to prevent them separating when you wriggle. This gives you a shortpad above the entry, turn and sit, place feet/lower legs in footbox of SB, lay back and lift in feet. I find that for spring/summer I don't need a pad under my feet to stay warm (and I sleep cold). I have used this down to ca. 35 deg f with a 20 deg f bag used as a quilt and been warm enough to be a bit sweaty under my back come morning. No glue is used. In the morning, separate the pads by taking out the acing, place together and roll to give a 20"xca.6" cylinder, lashed with the lacing lengths, for easy backpacking.. For car camping I use a 48"x36" pad made from a 72"x48" piece of small cell CCF pad bought by mail-order from a foam manufacturer (in the US, so not much use to you UK campers). Either way, I find the method easy, very effective from an insulation POV, comfortable and easily managed. As I said befoe, a bit of sweaty back in the morning, but not too bad. Protects from the wind, and is waterproof. Most of all, one blue pad from Walmart costs $8 over here so this is by far the most cost effective system you can find. The pads can also be used around camp, and at rest halts a sit/kneel pads. A final, much underestimated benefit is that the rolled up mat(s) can be a PFD if you are caught in a raging torrent of flood water, which you can't say for a down underquilt
