WHILE TOWING OUR FIFTH-WHEEL TRAILER WITH OUR FORD F350 DRW TRUCK, THE DIESEL PARTICULATE FILTER (DPF) CAUGHT FIRE. WHILE TOWING OUR FIFTH-WHEEL, WE TURNED FROM THE HIGHWAY ONTO A CITY STREET IN MESA, AZ. WE HEARD A LOUD "POP" AND THOUGHT WE BLEW A TIRE. AFTER PULLING OVER AND CHECKING THAT ALL TIRES WERE FINE, WE CONTINUED ON. WE NOTICED REDUCED POWER TO THE TRUCK AND THE TURBO BOOST WAS ZERO. WE PULLED OVER AGAIN TO LOOK FOR SIGNS OF A PROBLEM. WE LOOKED UNDER THE HOOD AND DID NOT SEE ANY OBVIOUS HOSES BLOWN OR ISSUES. THE TRUCK WAS STILL RUNNING, SO WE CONTINUED ON SLOWLY AS WE WERE ALMOST HOME. NEAR ELLSWORTH/THOMAS ROAD IN MESA, I GOT A NOTICE, "REDUCED ENGINE POWER," AS MY 14YO SON YELLED, "THERE'S SMOKE COMING OUT OF THE TRUCK." WE PULLED OVER AGAIN AND MY WIFE AND SON SAW FLAMES SHOOTING OUT OF THE TAILPIPE AND THE EXHAUST SYSTEM WAS GLOWING RED HOT. THE DPF WAS BLOWING FLAMS OUT TOWARDS THE GROUND. WE EMPTIED A FIRE EXTINGUISHER WITH NO EFFECT. OUR TRAILER HAS A WATER HOSE SO WE SPRAYED WATER ON IT FOR ABOUT 10 MIN TO COOL IT DOWN AND STOP IT FROM REIGNITING. WE DID NOT CALL POLICE AS MY WIFE AND I SHARE NEARLY 40 YEARS OF LAW ENFORCEMENT EXPERIENCE. WE EXTINGUISHED THE FIRE AND CALLED FOR A TOW. AFTER $10,000 IN REPAIRS, WE HAVE RECEIVED NO RESPONSE FROM FORD. WE HAVE NOT FILED AN INSURANCE CLAIM YET AND ARE WORKING TO CONTACT FORD AGAIN. FORD KNOWS THERE IS A PROBLEM WITH THE DEF/DPF SYSTEMS. DRIVERS HAVE NO INSTRUMENTATION TO SEE THE TEMP