I am working with a mutual aid org which has some resources at its disposal (money & labor) to help the folks who live there.
Of course, the people living there know best what they need, and with their current setups they mostly need wood for their stoves, or fuel for their generators, which are running electric heaters. But not all of them have stoves or generators.
I think the next most obvious option is warm clothing and blankets, which it seems like they have in good supply thankfully.
My org has done some building projects in the past and is considering doing more, possibly with a rocket stove type design, though I'm wondering if that's worth the effort, and our money/time would be better spent providing the residents with more food/clothing/fuel.
Handwarmers are good in a pinch. Carry some in your car if you got one and pass them out if you see someone out with a sign. It's a useful thing when stepping out for a bit.
Sounds like their encampment is better than some in my area, wood stoves and all that.