You're not getting enough air to the burner to completely burn the propane, it could be a malfunction, but probably more a partially obstructed vent. Go outside, take a bottle brush, clean the two furnace vents, and use a vaccuum to get the debris out of the tubes. Try again, if that doesn't do it, if you feel mechanically inclined, take the furnace out and clean the burner and combustion vents, if you don't think you can handle that task, then find a dealer or someone you trust to clean it for you. In all probability, it's not the furnace, just a combustion chamber obstruction.
If the trailer is 2 years old, the furnace may well still be in warranty. I think it's usually 2 or 3 years for the furnace, maybe longer for the burner box....
Check your paperwork, get a bottle brush and go for it