A few years ago, I found the ultimate deer stand. It was a shed that was built at the top of a coal mining operation. It had two windows that were 3' x 3" and had a door and a roof and walls and a floor and had a little table and chairs and a propane heater on top of a tank of propane.
Every year when I used it, I would put a couple of dollars in the basket for the people who bought the propane. I don't think that it used but one tank every 10 years - because you didn't have to burn the propane heater more then 3 hours a day and you didn't have to sit in the stand more then 3 hours to get a deer.
When I came back to use the stand last year the owners son complained that someone had broken in and had stole their spotting scope. I have a 15X scope on my rifle and I did not need to steal their cheap scope.
The next time I came to the hunting shack - the door was locked with a 1/2 inch bolt and a big padlock.
I burned a big hole in the sleeve of my hunting coat two years ago, reaching around the propane heater to shut it off. I didn't know it until I got home that night. The heater glowed red hot.
It kind of bummed me out - because I paid $250 for the coat.
In my tree stand, I use a old Kerosun heater and a wooden box - that I call my fireplace. It gets so hot in my tree stand that it melts the chocolate bars in my pockets. I have walls and a roof but no windows in my tree stand.
I would say that the best heater would be a Kerosun heater and to leave the heater in your tree stand all year long. That way the deer would become accustomed to smelling the Kerosene in that area and would not pay any attention to it after a while.