DRIVING 35 MPH AT WHICH TIME SMOKE BEGAN TO EMANATE FROM REAR OF VEHICLE AND QUICKLY BEGAN TO FILL ENTIRE INTERIOR. AFTER PULLING OVER, SHUTTING OFF ENGINE AND EXITING VEHICLE, OPENED BACK PASSENGER SIDE DOOR TO SEE FLAMES WHICH APPEARED TO BE COMING FROM UNDERNEATH BACK PASSENGER SEAT (RIGHT SIDE). WITHIN A MATTER OF SECONDS, FLAMES HAD SPREAD THROUGHOUT ENTIRE INTERIOR AND ENGULFED ENTIRE VEHICLE. VEHICLE WAS DECLARED A TOTAL LOSS AT THE SCENE BY ATTENDING POLICE AND FIREFIGHTERS.