2016 F-150 3.5L 4X4 ECOBOOST WITH MAX TOWING PACKAGE - VEHICLE SUDDENLY AND W/O WARNING CAUGHT FIRE AND ENGULFED IN FLAMES WITHIN 10 MINUTES OF HEARING A HUMMING SOUND AND THEN SEEING WHITE OR GRAY SMOKE. WE WERE TOWING OUR 28 FT TRAVEL TRAILER FOR THE FIRST TIME IN ABOUT 4-5 MONTHS, 30 MINUTES INTO THE TRIP ON A FLAT HIGHWAY. PULLED OVER WITHIN 1 MIN OF HEARING THE NOISE/ SEEING SMOKE. UPON EXITING, SAW FLAMES PEEKING OUT FROM UNDER FRONT OF TRUCK. FLAMES HIT THE CAB WITHIN PROBABLY 3 MINS LATER. WE HAD TOWED A 28 FT TRAVEL TRAILER WITH THIS VEHICLE EXTENSIVELY AND COMFORTABLY WITH FEW ISSUES (EXCEPT THROTTLE BODY FAILURE AROUND 30K MILES). REGULAR OIL CHANGES AND MAINTENANCE. FULL PA STATE INSPECTION 3 MONTHS PRIOR, OIL CHANGE 2K MILES PRIOR. NO OUTSTANDING RECALL WORK TO OUR KNOWLEDGE. NO UNUSUAL HANDLING, SMELLS, LEAKING FLUIDS THAT WE NOTICED, OR WARNING LIGHTS. FIRE INVESTIGATOR'S BEST GUESS WAS SUDDEN TRANSMISSION ISSUE BECAUSE IT COMPLETELY BURNED AWAY BUT WE'LL UNFORTUNATELY NEVER REALLY KNOW.