I was building them before you could buy them. Called it a coffin blind.
Someone finally built my design with modern materials.
The only difference is I made mine out of luan and builders foam.
The foot area on mine was bigger so I could put the dog at my feet and use a small ready heater. Did not bother with doors. Designed them blinds to fit me, dog, and heater. Not very portable but they worked. Scouting the path geese use helped me locate them in the right place. I quit using them but I bet someone does.
This looks a lot like what I built.