I just want to remind folks of something that worked super for me back in the day when I only used the SS. But I kind of forgot about it until recently. I never fully explored it's capabilities as I got side tracked into the Pea Pod and JRB MWUQ. Both of which work great, plus I was experimenting with non HH hammocks, so I kind of abandoned more research on the SS, even though I always thought it was a pretty good approach.
But lately I have played around some more with the Garlington Insulator(GI). Of course, it is still too hot to experiment with it. None the less, it is obvious it has great potential for the HHSS, or really any sort of UC, or even down in a Pea Pod.
The original GIs I experimented with consisted of a crinkled up, loosely folded space blanket "sealed" inside a garbage bag of various sizes. It adds very little weight or cost, maybe even zero if you rig it up from items you have with you any way.
What is the main problem with insulation in the UC of a SS, other than potential condensation? It is the elastics in the SS UC, which tend to conpress the insulation, particularly if down is used, as it holds the insulation against your back. In some spots, it may compress it down to almost zero. The SS was one of the 1st "snug" type designs: it holds everything just lightly against your back. That is fine with the HH pad or things like fleece, it is not enough tension to compress them much. But if you go stuffing fluffy stuff down in the UC or on top of the pad, they tend to loose a lot of their loft.
Why is the GI potentially great in a SS? First, the sealed bag is hard to compress. The light pressure caused by UC elastics will usually not cause any leak/compression. So, whatever you put in there to cause some loft ( a down jacket or vest or the original space blanket), whether 1/2" or 3", it will pretty much stay that way through the night. All though I think I remember that as the night grows colder, the air volume will shrink a bit.
Second, depending on how much insulation, it is light enough not to cause any sag in the UC. For ex, with just the space blanket, there will be zero UC sag.
Third, especially if using down, there is no concern with condensation for those that have issues with that despite using the space blanket on top of the pad, as everything is in a water proof bag.
I think Cannibal once said he puts one of those x-large zip lock bags in his pack as a liner. Yesterday, I took some of the Climashield insulation from my WB Torso UQ and put it in first a large garbage bag and later in a x-large zip lock storage bag. This gave me some significant additional loft under the pad, snugged up firm against my back. It would be easier to use with a zip mod or net free HH, so that you could position it after getting in. Flexibility might be a concern, with the garbage bag seeming more flexible than the zip lock. But I think it will be flexible enought o help, if you don't have too much air in there.
You might have to rig up something to keep it where you want it, though it has a tendency to sink to the lowest, and coldest, point.
Any way, some of us HHSS users might want to experiment with this this winter. I remember a pretty good boost just using the space blanket in a garbage bag, and I think it might also work great with more substantial forms of insulation. Folks ( including me) have successfully used insulation in the UC without bothering with putting it in a bag, but that compression does have to be accounted for. As well as condensation.