I use i small heater when i take my son if it's 30% or less and always try and hunt stands that are down wind from food plots. Never had a problem that i can remember cause most the time if its a shooter deer it never gets close enough to matter.
I've used the mr. Buddy propane heaters in box stands before. Had a mature buck come into the plot with it going. Its same smell as a Thermacell which I've used bow hunting and shot deer at 10 yds. Deer don't mind different smells. They mind human scent like B.O. more than unnatural scents
I picked up a Coleman 1500 btu heater and after reading that a lot of people use them I decided to give it a go and just turned mine on. I'm down wind of my food plots (8-10 mph wind in my face) and 15 feet off the ground so I think I'm good to go. I can only smell it if I put my face down to it. I read the smell goes away after the first tank