Just put a 30K BTU Procam Blue flame in my 7x27 trailer. So far, puts out plenty of heat. We'll see how it works when it gets cool out. Have the walls and ceiling insulated with 1" rigid, want to see how that works before I go to all the work of insulating the floor.
FYI, these heaters can't be bought in Canada. Theya re CSA approved for use in the US (Go figure?) so it seems like few will ship cross border. I ende dup buying them through a friend in the US. Northen tool has them on for $199 right now. Go to Greenline or Fairview and they will make a propane hose to whatever length you need. I don't plan to use mine too much, and for the cost vs. a furnace, I think it will more than suffice.