Not to second guess the fire department, but how could it be the converter if they were driving down the road as the photos clearly show.
My money is on the fridge being on and the fire starting there.
That looks like what is left of the fridge hanging out of the side.
I think I would have told the FD the propane was "OFF" too...
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW