The Enlightened Equipment Copperfield Wind Shirt comes in a 2XL and is supposedly sized a half size larger for layering. I have no personal experiences, but it may be worth a look.
https://enlightenedequipment.com/copperfield-wind-shirt-custom/
Maybe give a Seek Outside Gila 3500 or Divide 4500 a look? They’re integrated on the 24 inch Seek Outside frame and can handle 80 lbs. no problem. You can even add frame extensions for extra load lift if needed.
- - - Updated - - -
I forgot to mention that my Gila legitimately meets...
It’s probably worth mentioning that there are lots of weights of Xpac out there. I believe Kifaru uses VX21 on their Muskeg Packs and SG uses a heavier duty X42 on their frames.
Here’s an intro to Xpac from the Seek Outside website...
https://seekoutside.com/blog/xpac/
You can have Ron make your MLD eVent Soul Bivy with a full length, two dual sided pull zipper I believe. I think they’re running a 10% off Black Friday sale this week as well.
Why not just pick up a Seek Outside and be done with it? Their Gila and Divide both come in around 3 lbs or less and range 3500-4500 cu. in. (like the pack options you presented), but are also capable of carrying 100+ lb loads. You could even add a Revolution Frame Panel with compatible SO bag...
I think they referred to the Muskeg Bags as their “new ultralight bags” on Instagram.
Kifaru on Instagram: “Here’s a quick video outlining the features of our new Ultralight Bags! We should have these up for sale in the next couple of weeks!…”
Day One has fleece pants. You can get them insulated as well.
Pants (Fleece)
I'd email them and ask them to send you a fabric sample to see if it suits your needs.
For a new pack under $500, I would definitely give Seek Outside a look. Apples to apples, their Goshawk 4800 comes in slightly larger than the Metcalf, also has a load shelf, and weighs almost 2.5 lbs less (3 lbs, 11 oz per their website). They have plenty of other options under your $500 price...
I’m in the same boat. I love the minimalism and idea of a lumbar pack, but my stripped down SO Divide 4500 weighs just an ounce more, carries/flexes like a day pack, and can haul 100 lbs +.
I'm sure Nunatak could make you one. This was on their instagram... Nunatak Gear on Instagram: “11 oz double sided dog bed, measuring 38”x32” for hounds up to 50lbs. Synthetic Apex insulation with one side warmer than the other - and…”
I had a dog down coat made by them that my pitbull loves.