I did use a Big Buddy heater for a couple of years in my 10 x 6 lean-to hobby GH. I used a larger propane tank set outside of the GH. DH snaked the hose through a lower vented window into the GH to hook up to the heater. I was then able to insulate the window to keep out the cold. Now I have a natural gas heater mounted on the wall in the GH and that freed up some space. I mount a fan higher up on the wall above the heater to circulate the warm air. I wish that I could heat the GH with just the sun but it gets too cold here for an above-ground GH. Do make sure that any emissions from whichever heater you use won't harm the plants you have in the GH.
