That most definitely looks like a propane furnace, it looks just like the one in my parent's small Funfinder 139X. Rather than blowing heated air through floor ducts, it all blows out of that grill shown in the picture. Theirs does have a thermostat on the wall, so I'm not familiar with how else it would work if you can't find a thermostat. Also electric start without needing a pilot light. I think their camper is roughly 2000 vintage.
As far as what you see outside, their small furnace just has small roughly 2 inch by 4 inch metal plate with 2 holes in it (intake and exhaust? One of them is definitely exhaust anyway). "HOT" is stamped onto the metal plate.
Kind of like this if I remember right, I haven't looked at it in a long time.