Loc: Ozark Mountains in SW Missouri
Since you live in Texas and do some backpacking in Arkansas you might want to check out the campfire tent I made. It's based on the bushcrafter's "Super Shelter" design but made for backpacking. It's pretty easy to make too.
I've played with the candle heater concept a bit using tea candles and small disposable foil baking pans. I used 3 candles burning inside the tent, but I really cannot recall for sure how much gain in temp I got. I do recall it wasn't near as much as a campfire like the one in the video, but it was enough to demonstrate it works.
But that was an afterthought and this tent wasn't designed for that and doesn't have the room inside to fall asleep with one going so I've never tried it while camping. But it does demonstrate how to capture radiant heat and that's one of the keys to making it work.
So I believe is worth working on and using this reflective material one should be able to design something that's optimized for a candle heater. I was thinking something more like a bivy tent so you have less space to heat, maybe with an extended end at the head or foot to place the heater, perhaps behind a net to protect it (and me).
You need something to capture and radiate the heat from the candle too. As I recall, I used a rock with one of my tests, which we have in abundance here. My theory was the rock would store the heat and radiate more efficiently but it took forever to heat it up so that wasn't a good choice. A piece of aluminum sheet would work pretty good though, something the thickness of a cookie sheet would be durable enough.
I'm sure it can be done safely with good design and common sense. I've spent quite a few nights in my campfire tent all cozy and warm and wouldn't use anything else here now when it's cold out. But I would use one heated with candles.