i think you might want to look into how temp ratings work..
i *suspect* they are done at standard temperatures, pressures & humidity..
damp cold gives you pneumonia faster than dry cold, & damp windy cold is a misery that you will be aware of all night long..
i dinna know what a bivy sack was until i joined StP, but had been using a version of one (just a heavy plastic bag or closed tarp) for a good while before that..
also bought what *looks* like a bivy, but it's more like a fly-tent.. i think a bag over it would be super solid, but haven't tried..
Wiki points out a couple of things:
https://en.wikipedia.org/wiki/Bivouac_sack
the main thing is the inner condensation.. i was wondering how to describe that problem, & there it is..
& reading it, i see now that my thngy is a bivy shelter..
i have found, generally, that a good tarp over a mat of lufting vegetation (thin pine branches, dried grass.. hell maybe even tumbleweeds would be ok..) is a fairly good way to augment your sleeping base..
it's been a long time since having to do that (usually just look for a grassy spot). something over the ground is critical, when it is cold, in addition to any camping mat you may have.
make sure you have decent headgear, of course.. & if you carry a set of thermals, that could be a good thing.. i wonder if cutting the sleeves & legs off, to make them more easily peelable, would be a good idea..
short thermals for the day, long for the night.. sleep fully clothed, but just yank them off in the morning..
also.. keep a spare set of them fuckers in a ziplock bag.
carry a little clorox with you & wipe your feet & armpits & crotch & crack with about 1 teaspoon to a 1/2 pint of water, if you can't bathe.. microbial crap in your clothes fucks up it's insulating qualities..
dry mineral dust/dirt that can be shaken out doesn't hurt too much, but organic dirt retains water & tends to bind to fabrics of all types.. the last think you want in your bags is toe/crotch cheese, so take some sort of chlorine with you.. chlorine tablets are lightest & cheapest, but have the potential to chemically burn gear, so stow them in a bag inside of a small, heavy non-glass bottle.. keep the tabs away from your gear when working, because that powder is about as bad as the lead-sulfate from old battery terminals.. you may not see the powder, but it will make micro-holes in shit..
it also kill fucking bacteria, msra & about everything else it touches & is hella handy for some first aid & water sterilization.. i spray my unsealed first-aid gear with a chlorine water mist before bagging it, & keep a small, damp wad of it in the bag with them (suturing gear, implements & large trauma bandages).
anyways.. keep yourself clean, as well as dry..
the smell of organics attracts insects, so.. make yer choice..
also.. i posted about naphtha mothballs at one point.. carry about 5 with you.. crush one of these fuckers around your sack & it'll help keep the fuckers out..
i know this is winter in northern cali, so bugs may not be a big deal, but naphtha also burns incredibly, incredibly well, so they are worth it as firestarters, too..
rant rant rant... rave rave rave...
g'luck!
; )
C
