I will also add a few other tips I found that helped me stay still and longer on stands in colder weather
again I personally don't like goretex as a outer layer in VERY cold, it gets way too noisy for me, as it gets stiff and sounds like paper being wrinkled IMO
wool and fleece work tons better at staying quiet and flexiable, and wear a wind proof layer under it and no noise again , yet keeps you very warm
as for tips, I personally found using a kidney belt(started using them on MX bikes in the 80's when I raced) or a back brace that has the flexiable waist like band adjust!
they allow for longer sits as they help keep your back stronger, giving you better posture with less effort
THEN< you can also add a heat pack under them over your kidneys and lower back, and that alone adds a LOT of heat to your core temp, careful too close to skin they can even burn you,, but can make hours on stand a LOT more comfortable
and again, using a hand muff, and adding heat packs inside of that, will keep your hands a LOT warmer
if you do it right they allow you to keep your rifle in your arms and hands in side warm and super fast to then get rifle up if needed to, with little movements, or noise
placing heat packs with some duct take to the back of your neck can do wonders too, helps again on posture and not getting you a stiff neck if winds ot things cause you to bend to see in some directions
can literally take to ANY part of you you like then LOL
maybe some things others never thought of, as I have never really known anyone else to use the kidney belts like I do, or not until I told them about em and then m,any do so now LOL
and about any closed cell foam will work for a good seat, and you want CLOSED cell foam, it doesn't hold or absorb water then, if you can find it and buy two sections you can glue a piece of like ply wood in between then and never have to worry about small rocks or such poking thru , if you sit on the ground a lot
OR better yet, if you like to sit on the ground, , try taking and using a portable treetsand seat climber section ONLY
I have a few, I found the summits brand seat, on a lone wolf Wide climber, to about as comfortable as my lazy boy at home, when set up, add some shooting sticks and you can be set for some long shots with a steady rest
trick I found is strapping seat to tree a little better than just the supplied one's
so if you stand up or, it will never slide down or move, and the climber sections are a LOT lighter than a whole stand
allow you hand things off sides like bino's and calls or lunch and have it all handy and be extra comfortable