Heater Buddies come in 3 sizes: the single can size that it supposed to fit in a golf cart, the single can with the square burner, and then the big 2 can unit, I think they call that the Big Daddy or something.
I have the 2 smaller units, but have yet to cold season camp with them.
I also have a popup canopy with walls, but I've only used that in the summer to keep the wind and rain off the dog pen.
That said, your idea of using that as an outdoor heated space has merit - though I'm not convinced it will hold the heat all that well.
I am setting my TD up for some cold weather camping (ie. snow on the ground) the first time this winter. I will be bringing firewood for a big bonfire, and the smaller propane heater for either heating up the inside of the TD, or to huddle around under the canopy. I am also planning on the 1k generator, with the 350w electric heater inside the TD.
I think the last will be a very effective "cozy" space for sleeping. I figure during the day, it will be large bonfire for heat.
These are just my formative thoughts so far. I figure I'll survive, and then learn what to do for comfort to apply to subsequent trips. This is a winter hunting camp, so I expect there will be a canvas wall tent and woodstove somewhere in the mix.
In summation, no cohesive plan, just some related ideas to help kick around the conversation.