Good long johns help, along with a warm hat. Keeping your core well insulated is a good start.
Close enough?
View attachment 1078602
Close enough?
View attachment 1078602
The next size up “big buddy” has about twice the heat output plus a fan that runs off a D battery
I've got two of the "big buddy" heaters in my shootin' shack. They help a lot.
I just have the buddy but got my dad the big buddy. Now i gotta have one too!
I haven't put in batteries and tried the blowers yet. They're in a 20' Conex box with three fold down windows and spray foam insulation. With one window down it's tolerable as is.
I bet you could heat that with a candle. Wear your earplugs and put a chair in there for me.